They won't tell the difference at all from GH/tb/bpc in the OR. I'd continue those as well. Holding off on the reta is a good idea, especially if you have the RHR issues some get which could cause problems for your anesthesiologist. But also don't tell them you're on reta or any other unapproved "research chemicals" - it'll go in your chart you take street drugs and could cause insurance issues for you in the future - just say sema or tirz, which you definitely have a prescription for.
Shit, you ain't fastin until you're barely squeezing out a teaspoon of black tar once a week.