If you have Maximo for Transportation, where using PM relationships, you can say after the PM1 to deactive itself and activate PM2.
There is no other clean way of doing this. You have to have two different PM's because if you one PM the base freq=50hrs, so JP1 interval=1 (or 50 hrs, and JP2 interval=5 (or 250 hrs), however, Maximo will still generate the 100, 150, 200 hrs using JP1. This is not your requirement.
You need to have two PMs, PM1 @ 50 hrs and the other at PM2 @ 250 hrs, PM1 is active and PM2 is inactive, then when PM1 is run, it needs to be deactivated and PM2 activated.