Overriding

is it possible to override a default perm like pocketmine.command.gamemode?

 

what do you mean by override?

 

like change the default permission for pocketmine.command.gamemode

 

You can't change the command's permission, but you can set who is allowed to use the permission. [citation needed]

 

You could unregister then reregister the /gamemode command then set the permission if changing the permission for the command allowed usage is what your looking to do.

 

Like Michael said^

You can extend the command class you'll be registering while overwriting with \pocketmine\commands\default\GamemodeCommand.