It might be as simple as the Txxxx code being all by itself. I think if you place the Txxxx code on the end of a line with your desired position change, the turret will activate the new offset BEFORE moving to the coordinates, then execute the toolchange once it gets there. Example:
X5 Z8 T303
(machine uses offset 3 and moves to its X5Z8, then changes to pocket 3 once the turret gets there).
That's how our HL-2 does it anyway. It's a bit of an older lathe though so I can't speak to anything else without toying around with any of our newer machines.