I just want to note that I don't know how to achieve this: setting a GTK theme for Geany while still providing the user the possibility to change the pre-installed default. If we want to do this, someone needs to implement it.
For me it seems to work to have e.g. ``` c:\Program Files\Geany\share\gtk-3.0\settings.ini c:\Program Files\Geany\share\themes\Prof-gnome ``` (as the default theme) and then overriding it with e.g. ``` c:\Users\techet\AppData\Local\gtk-3.0\settings.ini c:\Users\techet\AppData\Local\themes\Windows-10 ```