Someone asked about GS while on a PD. Here's all that the contract has to say about picking up any flying while on a PD or APD, from sect 23I:

A pilot will not be awarded a white slip, GS, GSWC, IA, IAWC, yellow slip, or swap for
23 a rotation that is scheduled to operate on a day on which APD appears on his schedule.
24 10. A reserve pilot will not be awarded a GS, IA, or yellow slip for a rotation that is
25 scheduled to operate during a day of his PD.

Looks like a regular line holder CAN do anything he wants on top of a PD,
a reserve guy CAN'T,
and no one can fly on top of an APD day.