I think you do not need to manually add any keys...
if you want to add new filed, just make one starting on join form. System name is the lang key. Caption is whatever you want to show under that key.
So hit join page, add a block, edit it (system name, caption...) then go to other pages, EDIT,VIEW and SEARCH profiles, do the same (add blocks) using the sam system name and captions...under all options...owner, admin, moderator....
Thats how i did ti and don`t have any problems with it...
I hope this helps...
Nurke
