Time of day chart option in the COR... is an option. In the partition table specify the trunk to be used. Time of day chart 2 = PGN 2 etc... that is if you have partitioning.
If they only dial a specific set of numbers you can create a route pattern specifying the trunk, then in ARS program those numbers to route to the route pattern, which would then route out those programmed calls to the trunk you specified in the route pattern.
I'd agree with dufus2506, don't use TAC codes. They don't work with ISDN PRI's anyway.
If you do use tac codes, program them with ~s then your TAC, that way they don't see the code. Your basically given them the keys to the car, this method by passes CDR as well.
Thanks,
Wildcard