Thanks to a tip from The Composer (make it a story goal) and RestingLichFace who was kind enough to write the script it works!
So automated teleporting between levels in GM Mode now is possible.
The funny thing is that it even teleports a single player (who will be stuck in the destination level untill the GM activates that level) if you don't set the script to actually teleport the whole party.
He're is a copy of the script for those who like me don't script themselves.
INIT
DB_Redunzgofasta_Teleporters( <EnterEventTrigger>, <TeleportDestinationTrigger>);
KB
IF
CharacterEnteredTrigger((CHARACTERGUID)_Char,(TRIGGERGUID)_Trig)
AND
DB_Redunzgofasta_Teleporters(_Trig,_Destination)
THEN
TeleportTo(_Char,_Destination,"InsertEventNameIfYouWant",0); //change 0 to 1 if you want to teleport all characters in party)
Use an Event Trigger for the teleporter and a Teleport Trigger for the destination.
Don't forget to set the name of your OnEnter Event of the triggers to the name of your script!