I lost count of how many time exactly I replenished my 1000ml working solution of originaly XTOL-R with 70ml fresh stock solution of XT-3 after each roll, but I'm sure at this point that there's not much Xtol left. I also quickly forgot to test the PH..
I always develop one roll of 35mm at a time, and it's almost always fomapan 100. All I can say is that with the same times, I didn't notice neither over or undevelopement. In other words it ended up working fine for my purpose.
Please note that I do not know how much the activity of the working solution changed and if it was in the normal margin of a replenished workflow with Xtol or not. All I can say is that it didn't ended up as a catastrophic failure and my negatives didn't looked better or worst