I PVR'ed on APFS 75 prior to age 55 to compete to stay in the same post (the only one I was willing to remain in the Service to do) on FTRS terms.
I won the competition for the post by default (other applicants all withdrew when they found I was competing) and - after taking what was then the 1-month mandatory time out - carried on as FTRS on RFPS 05 terms.
I subsequently PVR'ed from the FTRS post when circumstances at the base changed dramatically, along with a dumbing down of the future intent for the activity I was engaged in, all coincident with my opportunity to emigrate.
My full AFPS 75 pension was restored immediately and I was sent a letter informing me that I would be entitled to an additional amount earned on RFPS 05, at what age I could apply and how soon before the relevant birthday I could submit the necessary form.
The claim process went smoothly and, after the first RFPS 05 payment, future monthly payments for AFPS 75 + RFPS 05 were combined.