No. SKSs in the PRK cannot have ANY additional evil features. Even attaching a Dragunov or thumbhole stock is illegal.
SKSs are imports. As such, not only must they comply with the federal '94 AW ban, the '89 and '99 PRK bans, but they must also comply with the '89 changes to the import provisions of the GCA'68.
Of course, if you spend another $100 or so in US-made replacement parts, you can turn it into a "domestic" gun, and then you can add all the evil features you want providied you keep the fixed 10-round mag.
Note: if you do this and are "caught", you'd better be able to prove you're using a gun built with enough US-made parts. The GCA'68 provisions ARE commonly enforced.