Replacement of Layout File

The Layout Files of a theme must be included within a def folder that is a child of the folder containing the corresponding themedefinition.xml. Inside this def, the folder path must be created to match that of the Layout File that is to be replaced.

Thus, when a page is to be rendered, if a theme applied to this page has a Layout File with the same path as configured on the page, the file included in the theme will be used instead of the original.