[qualiteam]

I've tried this locally and it works for me.

I'm attaching a sample module that will "decorate" Crisp White theme with its own "skin" directories. It changes the left sidebar menu template in the backend (so a new "Custom header" title appears above it), plus it makes some sidebar blocks in the storefront yellow (check a category page to see it).

I didn't try other "interfaces" (mail and common), but I believe it should be done exactly the same as I did for the "admin interface" (check the MainCrispWhite::getSkins() method).

Also, I've found that when you adjust getSkins() method of CrispWhite, X-Cart 5 does not include the new skin directories into the archive with your module files when you create one. That's why instead of placing new skin files into skins/my_custom_theme/... I split these into multiple skins/customer/modules/... directories (check the structure of the attached archive).

Does this work for you?