There is no Va law that I know of. The law that requires a Serial Number is actually an IRS tax code that Manufacturers must comply with.
The ATF has incorporated it into their regulations as part of licensing manufacturers.
Non taxable firearms like homebuilt guns are not required to have a serial number so removal isn't an issue. You just don't have to have one.
Serial numbers can be removed under certain conditions. For instance, if refinishing would remove it, the ATF has a form to fill out that you can have in hand during the refinishing, then the number must be re-stamped.
For firearms that don't have a number either because of age or removal, it can be stamped with an ATF Number. Another simple form to fill out and the last one I did, there wasn't a charge. That's been a while though.