IMHO it's pretty important that Maul = Grievous, and as much emotion and so on is put into Obi-Wan vs. Grievous as possible, because otherwise that battle just feels totally empty. Plus, Maul has form for effectively using more than one lightsabre at once. As with the headache in my ep1 as to the reveal of Padme/Amidala's dual identity, there's no reason, really, why Maul can't be called Maul in Ep1 and Grievous in Ep3. I would strongly favour renaming him in Ep3 to Maul, but that sounds eminently unlikely. Would it, however, be possible, to do Grievous's body armour over in a Maul colour scheme? I think that would totally rock. We love Maul, he's ace, and one of the few good things about Ep1. Let's keep as much of him in the PT as possible.
(Incidentally, my Ep1 as suggested by someone else, will feature Maul instead of Palpatine giving the orders to the Nemoidians, so he'll have a much bigger gravelly-voiced speaking part.) (If I ever get around to it)