Looking for input here on Bone-in ribeye

Carving the whole ribeye roast into individual steaks after cooking won’t be a problem with my electric knife. I’m just concerned that if I cook the whole thing untrimmed, that the outer layer won’t mellow at all and might get even tougher. For a fresh roast, I would normally slather dijon mustard all over it and then cover it with rub and then smoke it to an internal temp of 120-ish. Then let it rest for a bit and then sear the outside at high temp.

I was thinking maybe the mustard would somewhat rehydrate the dry-aged crust during the cook along with any rendering of fat.