If they reserved posts to get post quota that means post counting time is mostly ending. I am sure they will return a few minutes or hours later to edit their posts. Very likely that they make reserved posts for their farm and after they done with reserved posts, they will return to each account for editing.
I don't think they will spend days to come back and edit.
I would also say so if it had become a habit. But I won't think much about how to prevent it because if we come across such users then reporting to moderator is the key solution for handle with them. The habit may not be a violation for the forum, but the bad work ethic of the signature campaign participants is not exemplary.
Red tags are also not the right solution in such cases
[as they say], but it's probably worth expecting the maintainer to blacklist the violator and exclude him from future campaign. But it looks like this thread will change their habit of not getting caught, and it looks like we're going to have a hard time pinpointing the violator.