Don't think you can. If you can take yours apart you can paint it.
You have to take it apart
take apart the whole gun
Yes I have a bunch of airsoft gun's and i have used ammo that is the wrong size... and i clogged the gun and had to take it apart to get it out.
It will fall apart over time.
Check some of the bigger airsoft retail sites - most have a boneyard section where you can buy damaged guns for cheap.
I suggest that you start by finding old, used, or broken airsoft guns (or your own), and taking them apart, to find out how they work. Then, you would have to find a material to build it out of, such as wood or lego's. After that, all you have to do is put everything together, and hey presto, airsoft gun.
Best left to a gunsmith.
Ahh figure out what the problem part is than figure out how to take the gun apart and put it back together from YouTube, an airsoft forum, or from an airsoft website. Than buy the replacement part and put it in the gun. If the gun was bought for under $100 than you would be better off buying a new gun instead.
Installing a new piston involves taking the gearbox apart, so if you are not confident in your airsmithing skills, take it to a professional.
why does an eagle have a hooked beak
yes and they used it like owls they use their hook to rip apart their prey