Replo works just like a Shopify theme developer - when you publish a page, Replo creates content (page templates, sections, and more) which lives in your theme. This means that when you switch themes, you should consider whether there will be an impact on existing pages.
Replo detects when your theme is switched in Shopify, and as long as your pages are published in Replo, Replo will re-save all necessary assets to your new theme so that your Replo pages and sections continue to function.
It's good practice to make sure that there's no disruption to your site when switching themes by checking the main flows of your site to make sure they work, since new themes may introduce HTML or CSS conflicts which can sometimes cause issues with styles on pages which worked with the previous theme.
If you have a custom development process which involves switching themes very frequently, see Custom Theme Deployment for developer guidance on how to avoid disruptions.
You can also email firstname.lastname@example.org with any questions about how swithching themes works in Replo.
Themes and Homepages
When you set a page as your homepage, Replo automatically updates your Shopify Theme to use a copy of that page as the theme's homepage. When you publish a new theme, Shopify will use the homepage of that theme as your store's homepage, which might not be the Replo page which you previously set.
After publishing a new theme, if you want to make sure that a Replo page is the homepage for the new theme, make sure to toggle the "Is Homepage" toggle off in Page Settings, save the page, then toggle it on again and publish the page.