You can easily change your gamemode with the commands:
/0 = /gamemode 0
/1 = /gamemode 1
/2 = /gamemode 2
/3 = /gamemode 4
You don't need to add ANY new permissions.
The player only needs the permission to the "/gamemode" command and he can change his gamemode with EazyGamemode.
GitHub (for developers only): http://adf.ly/1XHLag