You can't really reserve definitions for hotkeys since anyone can define their own. Your best bet is to avoid defining hotkeys in your theme that are defined by default in a fresh ls installation.

If you are creating hotkeys in your theme you should define them in the themevars.rc file and document them in your readme. A disciplined LS user will know to look in these two files for information about configuring a theme.

"The OTS disallows modifying anything in the profiles/personal folder, correct?"

Incorrect. You can modify these files as you, the user, pleases, provided you only change the settings. As a theme creator you only need to realise what variables exist inside these files and do not create a conflicting setting in your theme. The theme creator does not distribute the personal.rc file in his/her theme so it makes no difference what changes he/she makes to his/her own personal.rc file. The idea is to not create a conflict.