Yeah, I replaced the body because the original didn't fill out the suit very well. I also knew that I wanted to replace the head anyway, and the Medicom body would've made that tougher (thinner neck and smaller neck peg than most 1/6 bodies). I cut the suit with a straight line down the spine of it, swapped to a thicker body that fills the suit much better, and re-sealed it. Unfortunately, the change didn't help much in terms of holding poses.
As far as I can tell, if you want to change bodies but keep the original head, you'll either need to match the neck style of the original or modify the head to fit onto neck pegs like those used by Hot Toys/Sideshow. Maybe others here know a simpler way, though.