UStik, I owe you an apology. I read more into your post than was there while I was in a bit of a mood and itching for a debate.

Rapptor, to be fair to your case I do agree that for most cases just switching things around and keeping the same CG is OK. And let's face it. Most general sport models within a close range of span where the wings will fit easily from one to the other are all roughly the same wing to tail area ratio and generally don't have radically different length fuselages. So if it looks more or less right then it'll fly fine.

But consider what is going to happen if you start swapping parts between radically different shapes. Such as put a 2 meter glider wing onto a Jr Falcon fuselage and tail. Or on more performance level models such as higher end sailplanes. If you do that and then want to trim the CG for best performance then all this stuff really does matter. But for general sport flying? Not so much and "close enough" is "good enough".