How do I customize my theme safely without risking updates breaking those changes?

Shopify Discussion

Topic summary

The original question asks how to customize a Shopify theme while preserving changes through theme updates.

Key Recommendations:

  • Always duplicate your theme first before making customizations (Online Store → Themes → Duplicate). Work on the copy, not the live theme.
  • Avoid editing theme code directly (the “Edit code” option), as manual code changes will be overwritten during updates.

Safe Customization Methods (Update-Proof):

  1. Custom CSS fields - Available in Theme Settings (applies globally) or individual section settings (scoped to that section only). Has some limitations on accepted code.

  2. Custom Liquid blocks/sections - Allows adding content, data processing, JavaScript, and unrestricted CSS. Can be placed in headers (runs on all pages) or specific templates (product pages, homepage, etc.).

  3. AI-generated blocks - Survive theme updates and their code becomes accessible under the blocks/ directory for review or enhancement.

  4. Apps - Most modern apps don’t break update compatibility, though some older ones modify theme code. Apps may impact page speed but are necessary for features like wishlists, back-in-stock notifications, and Instagram feeds.

All changes made through the Customize interface (not code editor) persist through theme updates.

Summarized with AI on October 24. AI used: claude-sonnet-4-5-20250929.
1

Hi,

I am Kamal Hinduja based Geneva, Switzerland(Swiss). Can anyone explain How do I customize my theme safely without risking updates breaking those changes?

Thanks

2

Hello @kamal123 ,

I hope you are doing well!

Can you please confirm what would you like to change? It depends on the requirements you have but to customize the theme, Go to Online store >> Themes >> Customize

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But I recommend you to take a backup and customize on that theme, to take a backup, go to Online store >> Themes >> Menu >> Click on Duplicate

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And customize on new theme

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3

Just never go to ... → Edit code :slight_smile:

Seriously, whatever you do in Customize will stay through your theme updates.

There are 4 main tools:

  1. “Custom CSS” in “Theme settings”. This CSS code will be output as is and will apply on every page of your store.
  2. “Custom CSS” in section settings. This CSS code will be modified to scope it to apply only to elements inside this section (this will also raise it’s priority).

“Custom CSS” may be picky about code you paste there. It does not tolerate, say page-width or content which limits your options a bit.

Also, CSS mostly responsible for the way how your site looks (and paritally, interacts), you can’t really add more information this way.

  1. “Custom liquid” blocks/sections – this is your legal tool for fetching data and adding content. Basically, you can add there whatever you may be adding into the theme code. Can process Liquid code, add Javascript snippets and add more CSS (this time, unconstrained). You can use Javascript to manipulate everything on the page, extend theme JS code, listen to JS events and react to them, load fonts and so on.

NB! You can put your “Custom liquid” inside Header/Footer groups and inside “Template” part of your page. Header/Footer are the same for all pages, so code you add there will run on all pages. Template area – code added there will only run for this specific template, say, only on product pages, only on homepage, etc.

  1. Finally – AI generated blocks. Funny enough, those will also survive theme updates. If you can force the system to generate something nice and robust, then you can use theme. NB from above applies to AI-generated blocks too.

Keep in mind that after you save newly generated block, its code is available under blocks/ path in your theme code, so you should be able to read it and correct your prompt or add some “Custom CSS”/“Custom liquid” to enhance it.

Also – apps. While some apps modify theme code and break its ability to update, most modern apps behave. Unfortunately, you can’t tell which apps are which.
Generally, Apps tend to negatively effect page speed, but some things can’t be done in theme code. Say, “Wishlist” (proper, which will work on multiple devices), “Back in stock” and “Instagram feed” are some of the things which require apps.

Some apps which edit theme code provide their own tools to assist with theme updates.