I presume that with "you build your theme", you mean you created custom templates, stylesheets, etc. As long as these templates inherit the templates from the website modules (e.g., website, website_sale, website_blog), all pages on your website will be affected, but the content will remain the same. Check out my blog post about installing, updating and uninstalling website themes for more information:

Website themes in Odoo: Install, update, and uninstall made easy

I hope this helps!