Does anyone know if it is possible to assign an alias / label to a control channel frequency on the 396?
You can name the Trunk system anything you want, but as far as the Control channel is concerned, it is a pointless thing to do. The scanner just listens to the Control channel and switches to a Voice Channel when a transmission takes place. Also most systems have more than one Control channel that the system rotates on a regular basis, not all of them, but most.
But if you wanted to do this, you could possibly do what you are asking.
If the system does have more than one Control Channel, just put ONLY ONE of them as a trunk system. The Second Control channel you could make another system and call it what ever you wanted, and so on....
So if your system has 4 control channels that it rotates through, make 4 individual systems and name each system whatever floats your boat. You would have to do a lot of duplicating when it comes to you Talkgroups because each system would have to have the same ones in each system you created.
That would be the only way I could see you doing what you are asking.
If you do decide to do it this way, make each system have the same Quick Key number. That way all you have to do is hit one number and have all of the systems you create for the ONE trunk come active. It will only lock on the active control channel and ignore the others until it rotates to the next one.