I did my IR(R) after an EASA CPL - we found at the time a clause in the regs somewhere that said I therefore didn't require the IR(R) TK written exam - it might be worth wading through the regs to see if that applies to an MPL holder also. I can't see that they have done any less TK than I had done, but I can't recall the exact wording. It *might* have said "professional licence", but I'm really not sure.
G