Swapping parts alone always drove me nuts. Always one arm that's perfect, then seven that are close but not quite, and none are really any better than the other. It's actually easier for me to make a whole new appendage than to adjust an existing one to suit.
Perhaps a little advanced for you at this point, but this is something to consider. I keep poorly sculpted 1/35 figures (like those reeeealy old Tamiya figure sets) in my parts box soley for the purpose of stripping the uniforms and all other detail, then I can use them as armatures to create whatever pose I need, then I re-sculpt the detail to suit. You're pretty much scratch building at this point, but once you get the hang of it, it gives you incredible freedom of subject matter and posing. In 1/35 scale I use sprue for arms and legs, carving them to a basic "nude" shape and pin the joints using sections of paperclip. I then use stock heads, hands and boots to finish them off.
I use Magic Sculpt for all sculpting work, but Miliput, Hexcell A&B Epoxy Putty, Duro Epoxy Work equally well. Spot putties like those from Squadron will work too, though I find them troublesome for more than filling gaps in joints (like those found after chopping and arm at the elbow to reposition). For re-sculpting the uniforms and fine detail, you're better off with an Epoxy putty. Epoxy takes about two hours to cure fully, but you can kick it off in about ten minutes with a simple oven made from a box lined with aluminum foil, with a 60 light bulb for a heat source. You have to be careful if with styrene though, as it can melt a little during the heating process if you aren't careful.
Keep another figure close by to use as a scale reference too. Especially if it has the type of uniform, or elements of it, but it's mainly for proportion. You'd be surprised at how easy it really is with a little practice. The Shep Paine book, mentioned above, as well as his Diorama book are a wealth of info on the subject. Bill Horan's Military Modeling Masterclass is worth a look as well.
As I said, perhaps this is a little over your head at this stage, but give it a try, you never know. Plus you can use lesser elements of this technique for simpler modifications, like creating a new arm or leg for a stock figure.