My apology if there is any negative interpretation on my previous comment. I'm sure you're very skillful, but the problem I've pointed out has nothing to do with the modeller's skill. You said you've been told something, have you ever tried it yourself? What I've pointed out is something that we gundam modellers learnt the hard way over the years (and agreed by a fellow gundam modeller too).
If you want to avoid painting stuff that won't be seen, you really don't need to assemble the gundam and disassemble it again. The instruction, google and your experience will do just fine. But if you don't mind breaking some pins and end up with some chipped / deformed edges or corners on the parts, nevermind.
Some may believe that we can always glue the parts so nevermind the pins, well maybe true on scale model, but absolutely not true on gundam kits. I like your idea with nail polish on loose poly-cap, in fact I did the same trick 25 years ago, but sadly many joints and moveable parts on a gundam model can never be repaired, especially after the model is painted and finished.
Even the latest and much smaller RG kits have issues on the durability of the joints and even the plastic itself (joints failed or parts broken right after finish, can't even hold its own weapon, parts keep falling off the model etc), let alone the much larger, heavier and older PGs. That's why it is not a good idea to assemble the model and disassemble it again just to see which part won't be seen after assembled.
Anyway, good luck with your PG kit, have fun, and have it your way.