Max,
Just done exactly that myself, and now on the IR, the only effect it has on the IR is the hours of training required. You would have to sit the 55hr hour IR as oppose to 45hr with a CPL issued. If you have access to some nice cheap flying it may work out cheaper to fly 20 hours extra hour building rather than another 10 in a twin/simulator (depending on how your school breaks it down). For me it broke roughly even, so I elected to shorten the time scale and get on with the 55hr course.