If the gun is legal as it sits now, then you're good to replace any part with a made-in-the-USA replacement part.
The "point" thing is an awkward way to look at it, because the "point" system typically looks at it backward. From the following list, a semiautomatic rifle or shotgun can have no more than 10 foreign-made parts.
(1) Frames, receivers, receiver castings, forgings or stampings
(3) Barrel extensions
(4) Mounting blocks (trunions)
(5) Muzzle attachments
(7) Bolt carriers
(8) Operating rods
(9) Gas pistons
(10) Trigger housings
(15) Butt stocks
(16) Pistol grips
(17) Forearms, hand guards
(18) Magazine bodies
Not every rifle has all twenty of those parts (for instance, not every gun has a pistol grip or a muzzle attachment). So people try to work the wrong way, saying that since an SKS has 17 of these parts, you have to have 7 US-made parts. But that's backwards.
You can have no more than 10 foreign-made parts. Your SKS can have 17 US-made parts and zero
foreign made ones. That's totally legal. You just can't have 11 or more foreign-made parts, no matter how many US-made parts you have.
Tapco, one of the US-based manufacturers of compliance parts, explains it more fully here: http://www.tapco.com/section922r/