This article explains how to prevent your users from changing their theme style within the cPanel User Interface.
The following explains how to prevent your users from changing their cPanel theme style.
Disabling the ability to choose a Theme Style
To disable the "Change Style" feature, you'll need to access WHM » Home » Packages » Feature Manager » Edit Feature List.
Once there, select an existing feature list or create a new feature list and ensure that the feature "Change Style" is not selected.