Of course, you certainly can. It is really up to you as each would option requires differing amounts of cash and waiting time.
Three are three options actually:
1. Have the existing incabloc modded to have the Y-notch (would depend on the availability of a rep-friendly watchsmith who can do that)
2. Buy the Y-incabloc mod from the TD and have it replaced by a watchsmith (again, would depend on availability of rep-friendly watchsmith)
3. Sell the existing PAM111 and buy a new one with the Y-incabloc mod (this would be the easiest route, it would depend if you're willing to wait for the existing 111 to sell or you can buy a new one without waiting for the sale)