If they are using a TG on the RWC, or Maricopa County, trunked system, not only would they have to switch to a different channel, they'd have to switch to a different deck, since I don't believe they can have two different systems in the same deck.
If channel 1 is on A-deck, channel 2 would have to be on B-deck, for example.
The other possibility would be a conventional repeater for channel 2 on A-deck. They can mix conventional channels in with a trunked system on the same deck.
(Bank--deck--group--zone. Different terms for the same thing. Deck is the term used here.)
John
Peoria