Scheduling has always had wide lattitude (i.e. no PWA langauge on the topic) to assign rest to reserves. There is also absolutely nothing that prevents them from removing an assigned rest period. The key though is if the pilot acknowledged the rest period there must be some form of notification of the removal (barring the pilot self-acknowledging). Most of the time it is somewhat irrelevent. For example, say they have 5 RES pilots Tue-Thur, all with a golden X day Friday, so they all have pre-posted rest at 0600 on Thursday. Now a 3 day trip hits OT that releases at 1800 Thursday. CS will absolutely remove that rest period on a pilot to assign the rotation. It's not like they are going to send it out to GS in order to protect rest 3 days out. But here's the kicker that is really jacking things up: say now there are those 5 junior pilots with pre-posted rest, and then a 6th senior pilot who does not have a golden X day on Friday so no pre-posted rest. Scheduling is skipping the 5 junior pilots with "assignments" and giving the rotation to the senior pilot. Again nothing in the PWA says they have to remove a rest period (even a pointless one) in order to assign a rotation in seniority order. They will generally only start removing rest periods when there are no other pilots without rest periods legal for the trip.