Not sure it is a functional work around, but someone mentioned hacking a POL plan but using Plan Builder to add a full plan. Then editing the individual phase from the calendar annotation, which allows you to change the precise plan applied. They were able to swap to a POL one in that case.
However, we don’t know if it will actually work with AT for Progression Levels & Adaptations at this time. Could be worth a test for anyone willing to play around.