Paid: Gameserver RCON Command upon member upgrade

Hey all, I'm looking at adding some functionality (and convenience) to our forums. We run a Garry's Mod gameserver, and offer ingame benefits for donating.

We're using the account upgrade system built into XenForo, and we're wanting to extend this so that when someone successfully sends a payment, it automatically sends an rcon command to the gameserver to set their usergroup properly.

On upgrade, it should send the rcon command to update their group, same with downgrade, just the opposite.