I did a gradual introduction of new clubs after becoming Master and I think that eased the transition for me. I had bought the Raptures as a pro and was familiar with them
I first upgraded driver and 3W. For a while I carried both the R9 driver and Rapture driver and used used them selectively depending on the course and hole. Then I upgraded wedges and putter. I added the Pro Raptures irons when they came out and then went to the G10 driver and eventually, new wedges again.
Learning my new clubs during practice rounds, especially the wedges, was critical to me. And it didn't affect my average.
Getting the new driver first put me approximately in the same area of the fairway as when I was a pro. (but the R9 also put me in some places I had never been!) I think, if memory serves me, I made master before the v. fast greens were introduced so I didn't deal with that issue right off the bat.
Oh yeah, forgot, I was promoted to Master when that average was only 67+. Its since been lowered to its current threshold.
To answer your question, it didn't take me long to get back down to my 67+ average, and I don't think I ever slipped back into the 70s.