It’s not as simple as a choice to return to previous pension or transfer to 15. People have made life choices on the back of the migration to 15. Whether that be to leave because of erosion of benefits or to allign to NEM and serve to 60, this was done in good faith and now the goalposts are about to change.
If you have recently accepted PAS then you have agreed to serve to 60, however reverting to 75 or 05 now means you can leave at 55 with a PVR penalty on 75, or not with 05.
None-the-less with a reverted AFPS retirement age of 55 then service beyond that date is now
on continuance terms and not NEM and will need to be renegotiated if you want to do so. Otherwise 55 is your new retirement date and I guess it will be even if a ROS for a training course extends beyond. The AP says an ROS can not extend beyond retirement date