Yes, there is an app for that: https://appstore.home.mendix.com/link/app/106033/TimeSeries/StyleSheetSwitcher
This way you can give each customer its own stylesheet. Works perfect.
Regards,
Ronald
quite easy to do now with the Maui9 framework
https://www.youtube.com/watch?v=VfDWCfLn128
Hey.. you can also use CSS Selector Widget for the Purpose. Based on the logged in user, we can configure different Style sheets.