I'd like to do the same. For instance, some folks don't like round avatars, so I would override the CSS for that. Other folks want zero color, so I'd make a monochrome skin.
Turn off Skin in Persona Theme
How to turn off user choose skin in Persona Theme?
You can hide the option via custom CSS. I'd like to remove it eventually for good, although lots of people still use skins
@paopevil Go to ACP -> Settings -> User and enable the option "Prevent users from choosing a custom skin".
@pichalite Thank you! This working!