Changing templates afterwards possible?

I am creating a WP site using Enfold for a customer which is not really IT affine. I am designing and setting up everything for them but as my customer needs really much content on his homepage they need to integrate text and pictures on PAGES (multi-levels) by themself. As I already mentioned they are not IT affine I have created page templates so they are able to integrate content just by changing the text/picture of each grid, slider (or other elements I used). Now my customer asks me if it is possible to make changes to all sites using this page template afterwards. Or is it even possible to make the same change (for example color scheme) only on the last level of the breadcrumb?

Thanks in advance!