a) Yes, Mediaportal needs to know how to handle the toggle bit. My understanding (which may be wrong) is that Mediaportal does know how to handle Nokia protocols, and so presumably it does know how to handle the toggle bit. I expect that the Mediaportal documentation explains how to send common IR protocols like NEC or RC-5/RC-6, and I suppose that it also tells how to send Nokia.
b) If you can't make that work, it is possible to modify each IR code so that we send two Nokia32 signals on each button press. The first one is chosen (perhaps by trial and error) so that it is recognized by the Pace as a possible IR command, but one which has no effect on the box (basically an unused function code). That will presumably reset the toggle mechanism. The second Nokia32 signal will be the desired function code. That trick works for many IR protocols that use a toggle bit; maybe it will work for Nokia also.