When a module is loaded from inside GiD, module can not control theme configuration.

But if you are installing GiD together with your module, there is a variable inside scripts/ConfigureProgram.tcl to control how GiD manage themes.
The variable is ::GidPriv(ThemeSelection), and its value can be:

1 (by default), user can choose the theme selection
Any existing theme (Example: GiD_classic), user will be forced to use this theme and options on menus and windows about themes will be disabled.

With this option its possible to obtain a package gid+module totally customiced with your prefered visual aspect.

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