I don't see the point to only one retraction. But I also don't think it changes the game in any appreciable way.
I don't get limiting the medic's role. It's hard enough without limitations like that.
To me it is not fair that the mafia doesn't get a shot at the spy without hitting the medic first. Otherwise the medic just protects the spy every night. And if we allow RCing then the spy can claim right away and start revealing investigations...that ruins the game IMO.