The moderators do not control this process. There is an automated serial vote detection algorithm.

AFAIK, under no circumstances can a Stack Exchange moderator reverse a vote.

More info on the serial vote detection process here: http://meta.stackexchange.com/questions/126829/what-is-seria...

edit: I just looked at your profile and the deletion/banning of a user account will remove rep too, so I suppose in that manner a mod can "reverse" voting, but it's all or nothing. They have no way to flip individual votes.

edit2: Moderators are not employees of Stack Exchange, they are volunteers elected by the community. Of course employees can change whatever they feel like. This discussion is about the moderators.