If you are going to do something like this, the military force match way was to line out the old s/n without removing it and then stamp the new one preferably in a stamp type that does not match the receiver s/n font. That would make it clear that the current trigger group functions with the rifle. Also, there is enough stacking tolerances in an SKS that I would suggest that you ensure that the trigger group functions safely in its current rifle as by swapping the groups one might accrue some liability if the firearm is rendered unsafe and sold to another.
Two reasons that all matching serialized firearms obtain higher prices is that 1) the condition is more rare and more desirable as the militaries did not care about maintaining whole parts assemblies other than for going bang and 2) there was a significant degree of hand fitting parts so that a "parts" rifle might very well be a) unsafe, b) rough in operation, and c) suffer mechanical malfunctions due to ill fitting parts.
Sometimes you get all three in something like a Luger as these had a significant degree of handfitting at the factory and Lugers have a more limited tolerance for operational problems on a good day. I suspect that a fair number of rifles like sniper types or more rare k98's might also have this problem especially after the flood of low priced Yugo and Russian captured rifles were imported.
Like other collectibles that soar in price, this has caused a big problem in collecting Lugers due to fraudulent markings, counterfeiting, and parts switching.
