The frame will obviously accommodate 559 rims, and swapping from racing calipers to touring ones will fix the reach issue, but who wants to fit MTB wheels to their race bike?
My second point (no 650c frame can accommodate an extra 5-6mm?) was about the extra 5-6mm needed for a larger wheel, not smaller.
Springdank may or may not be racing, but I was approaching the question from a feasibility standpoint, not about how much slower these changes might make the bike.
I assumed longer reach brakes would be required for the smaller wheel - no 650c frame can accommodate an extra 5-6mm?