Why not just up the volume of your main work? If you're just looking for overall muscle mass, the powerlifts fit the bill. Granted they may or may not give you most balanced physique. Then just use assistance to fill in the gaps and work on weaknesses and for pre/re-hab.
Is it because the main lifts are hurting your joints. Are you just getting a little tired of the main lifts and wanna do something different? Do you have some glaring weaknesses or imbalances?
If so, I'd do this instead. I'm thinking it would just be best to reduce volume, frequency, and/or intensity of the main lifts and use that energy you spare there for your assistance work.
What your doing is pretty drastic and I don't think it's a good idea unless you've developed some really serious imbalances over a period of years. And again, I'd only do this if your comfortable with the main lifts.
There are some big name PLers who in off season would do high bar squats instead of their stronger low bar, but that usually had more to do with sparing their shoulders and back than anything.