Need help with setting permission groups

Permissions I'm talking about: 3.1.x

On our server, we want users in group Default to have access to a command that will set them in a specified group.
For example, the command would be "/racepick dwarf", and you're moved to the Dwarf-group.
Now, you won't be able to change race again.

Further on, admins are supposed to have a admin command, that would change the race.
Example: "/racepickadmin Player Elf".

Now, since we haven't found a plugin that suits us, we decided to make our own, the other admins and I.
So, I wonder, is there a method that allows for group-changing (I belive so), and what's it like?

Bump :3

We found it, here if someone is interested
https://github.com/TheYeti/Permissi...rc/main/java/com/nijiko/permissions/User.java

EDIT by Moderator: merged posts, please use the edit button instead of double posting.