Good posts ST, I like you're thinking
I suspect that the ABS ECU is calibrated to cope with a 5-10% variation in tyre size front/rear for the purpose of accommodating normal wear & replacement at different times, even a 190/55-17 on the rear. However, the gen 1 rings (60/50) on your bike with the gen 2 ABS calibration (48/45) you now have, represents a variation of 13.2075471%. Well, that's my thinking.
The other thought that comes to mind if fitting gen 2 rings is the TC lamp on inst cluster factor. As the gen 1 ZG doesn't have it but the gen 2 ZZR apparently does (like gen 2 ZG presumably), there may or may not be an issue with that, just surmising.