Can an amendment to an amendment be made during the NCS?

Yes, as long as the amendment to the amendment remains in scope or does not change the intent as presented originally by the National Board.  This can be done by a national delegate making a motion to amend the proposed amendment during the Session.  An amendment to an amendment requires a majority vote in order for it to be the revised amendment which will then be voted upon to enact.

Source:  Constitution/ARTICLE XVII AMENDMENTS