if the goal is to make 4K77 look closer to the 4K UHD official release
I think the goal is simply to make it blend, by hook or crook. You could also add grain to the UHD in order to make it blend better with 4K77. And you’ll have to add grain to the UHD, at the very least to cover up the frozen grain, but also because to most observers, the whole thing is too far gone in the DNR direction.
But that doesn’t mean you have to make everything as grainy as 4K77, you could degrain one, and regrain the other, and meet in the middle. I expect that’s what’s likely to happen.
Beware temporal degraining – aggressive use of this technique is likely what led to the frozen grain plaguing the UHD’s. But in moderation, it could be useful.