The indexes in this enumeration are used for config loading/saving. If you add in the middle old configurations will no longer apply and will be loaded incorrectly.

I see three options:
* Use uiUpdateCounter to update the format (be careful though, it'll be 0 on first run regardless of version). 
* Only append to the enum. You'll have to uncouple display from enum order though
* Convert the index based saving to a real dict and only use the enum during runtime

I guess those all have their pro's and con's ;)