Learning by doing: Implementing a proper theme removal

[BdN3504]

Read about my feature idea in the corresponding thread.
I haven't been able to get anyone to tell me where to start, so this is my "call for help" thread. On the side line, this thread can encourage users, who think they have a decent feature idea translate it into working code.
The first thing i don't know is which files i would have to alter (after having looked at the source and different patches targeting similar features, i have come to think menu.c and settings.c are the files to look into).  Patches always start with which files they are altering, that's why i am asking this question. But if this kind of approach is totally wrong right in the beginning, please tell me. All i want to do can be found in the thread i already posted.
I am eager to start learning!

[bluebrother]

Wouldn't it be better to implement such a feature as a plugin, since it's nothing one could consider core functionality? The idea is to have Rockbox Utility deal with that issue, but that requires installing the themes using Rockbox Utility, which in turn requires the theme site getting finished ...