I certainly wouldn't hesitate to modify the chokes on the 20ga which has already been removed from collector status by being reblued and refinished. I don't like screw in chokes so would choose to have fixed choke opened to skeet. The way you stated condition I am not sure whether the 16ga is refinished or not. If it is refinished modify the choke. If original and not useful to you - sell it. Personally I would have no problem modifying the choke on that one either - but then I have been known to open chokes on Parkers and other classic doubles to suit my needs.
