Switching Shopify themes: what happens to your galleries

A new theme is the one change to a Shopify store that touches every page at once, and it is the moment people discover which parts of their setup belonged to the theme and which belonged to them. For a gallery app the question is blunt: after the switch, are the photos still there, and is the page still there? With Snug Gallery the first answer is always yes and the second is yes with a short list of things to redo. This guide separates what carries across on its own from what lives inside the theme and has to be set up again, and gives you an order of work for publishing day.

Two kinds of data, two different fates

Everything about a gallery in Snug Gallery is in one of two places. The gallery itself, meaning its title, the images and videos, their order, alt text, captions, links, hotspots, tags, the layout type and the customer-photo settings, is stored as app-owned metaobjects in your store, with the files in your store's Files library. None of that is in the theme. You could delete every theme in the store and the galleries would still be listed in the app, exactly as you left them.

The presentation of a gallery on a given page is the other kind. When you add a Snug Gallery block to a template in the theme editor and set its columns, gap, image shape, caption style, hover effect, lightbox options and custom CSS, those values are written into that theme's JSON template file. They belong to the theme the same way a banner's text or a featured collection's heading do. A new theme has its own template files and knows nothing about the blocks you placed in the old one.

So the fate of a theme switch is already decided by that split. Content survives untouched. Placement and styling do not come across, because they were never ours to carry; they were the theme's. The rest of this guide is about how long the second part takes to rebuild, and the honest answer is a few minutes per page.

What carries across without doing anything

The complete list of what you do not have to touch: every gallery and every item in it, including the ordering you dragged into place and the sort mode you picked; alt text and both caption fields on each image; links and whether they open in a new tab; product hotspots and the products they point at; tags and any tag filtering you set up; video embeds; the customer photo settings, meaning whether submissions are on and whether they are auto-approved; approved and pending submissions themselves; and the plan you are on. The gallery picker in the new theme's block lists the same galleries, in the same order, with the same names.

The images themselves deserve a sentence because this is where other gallery setups go wrong. Snug uploads to Shopify Files and renders from cdn.shopify.com, which is the same place your theme's own images come from. There is no second host, no app CDN and no theme asset folder involved, so a theme switch cannot break an image URL. The guide on where gallery images live goes into why that choice was made.

What lives in the theme and has to be redone

Blocks. Each place a gallery appears is a Snug Gallery app block in a section of a template, and the new theme starts with none. You add the block again on each page, pick the gallery from the dropdown and the content appears instantly. If the old theme had a gallery on the home page, one on an About page and one on a lookbook page, that is three blocks to add.

Block settings. The thirty or so presentation options covered in the block settings reference reset to their defaults in each new block. In practice most placements change three or four of them, so this is quick, but if a page relied on a particular combination, such as Masonry with four columns, no gap, Overlay captions and the lightbox off, write that down before you switch. The old theme keeps its settings for as long as you keep the old theme in your library, so you can always open it in the editor and read them off.

Custom CSS typed into a block. This is the setting most often forgotten, because it is at the bottom of the panel and was probably written once and never looked at again. It moves with nothing; copy it out of the old block and into the new one. If the same rules were pasted into the theme's global custom CSS instead, they are also gone, because that box is per theme too.

Alternate templates. A page or blog post template you created so a gallery could appear on a particular page is a theme file. The page itself remembers which template name it was assigned, but if the new theme does not have a template of that name the page falls back to the default. Recreate the template in the new theme with the same handle and the assignment comes back to life without editing the page.

Section placement around the block. Where the block sits in the page, what heading sits above it and how much padding the parent section adds are all the new theme's decisions. Expect a gallery that was flush with the page edge in one theme to have margins in another, and vice versa; that is the theme's section wrapper, not the block.

A table to keep handy

Survives the switch, no action needed: galleries, images and videos, order and sort mode, alt text, captions, links, hotspots, tags, customer photo settings and submissions, your plan.

Has to be set up again in the new theme: the block on each page, every block setting, custom CSS in the block or the theme, alternate page and post templates, the section wrapper's heading and spacing.

Partly carries: a page's template assignment, which comes back once a template with the same handle exists in the new theme; the customer photo submission form, which is part of the block and appears again as soon as the block does, with the same settings.

Do it in the unpublished copy, not live

Shopify lets you install and customise a theme without publishing it, and that is where all of the rebuilding should happen. Open the new theme in the editor from the Themes page, add the blocks and set them up while shoppers are still on the old theme, then publish. If you do it the other way round, publish first and add galleries after, the pages are empty for however long it takes you, and a lookbook page with no photos is a bounce.

The one catch is the theme editor's preview: the app block renders from the same metaobjects as the live store, so what you see in the unpublished theme's editor is the real gallery with the real images. There is no separate preview state to worry about, and a change to a caption in the app shows up in both the old published theme and the new unpublished one at once.

An order of work for the day

First, in the old theme, open each page with a gallery and note the gallery name, the handful of block settings that are not defaults and any custom CSS. A screenshot of the settings panel is enough. Second, in the unpublished new theme, recreate any alternate templates with the same handles. Third, add the Snug Gallery block to each page in the same position, pick the gallery, apply the settings and paste the CSS. Fourth, preview each page on a phone as well as a desktop, because the new theme's breakpoints will differ and the columns setting that looked right at 1440 pixels may want a change. Fifth, publish, then load each gallery page once on the live site and click into the lightbox. The whole process for a store with three galleries is under half an hour, and most of it is reading off the old settings.

If something looks off after publishing, the usual culprit is one of two things: a theme section wrapper applying its own max-width or padding around the block, or a template assignment that did not come back because the handle differs by a character. Both are theme-side fixes and neither involves the gallery data.

Theme updates versus theme switches

Updating a theme to a newer version of the same theme is gentler than switching. Shopify's update flow copies your templates and section settings into the new version, so blocks and their settings normally come across with it; what it cannot copy is anything you edited directly in the theme's Liquid or stylesheet files, which is one more reason to keep gallery styling in the block's own custom CSS rather than in a theme file. Still, treat an update like a small switch: check each gallery page in the updated theme before you publish it, because a theme vendor occasionally renames a section or changes a wrapper's spacing between versions.

Frequently asked questions

Will my gallery images be deleted if I switch Shopify themes?

No. Snug Gallery stores galleries as metaobjects in your store and the images in your store's Files library, neither of which belongs to a theme. Switching, updating or deleting a theme leaves every gallery and every image exactly as it was. Only the block placements and their presentation settings are part of the theme.

Do I have to re-upload photos after changing my theme?

No. Add the Snug Gallery block to the page in the new theme, choose the same gallery from the picker and the photos, captions, hotspots and order appear immediately. Nothing is uploaded twice and the file URLs do not change.

Why does my gallery look different in the new theme?

Two reasons, usually together. The block's settings reset to defaults in the new theme, so columns, image shape, caption style and lightbox options need to be set again. And the new theme's section wrapper adds its own padding, max-width and heading styles around the block. Open the old theme in the editor to read the previous settings, then match them in the new block.

Can I keep the old theme as a backup?

Yes, and you should for a few weeks. An unpublished theme in your library keeps its templates and block settings, so you can reopen it in the editor to check how a gallery was configured, or republish it in a minute if the new theme has a problem. Shopify allows up to twenty themes in the library.