When reviewing new posts I sometimes encounter questions that are tagged incorrectly, but other than that require only minor corrections or no changes at all. I have made a few suggested edits only changing the tags (and possibly correcting one or two spelling mistakes while I'm at it), and some of them have been approved (maybe wrongfully so). I have a couple of rejections though with the motivation
This edit is too minor; suggested edits should be substantive improvements addressing multiple issues in the post.
From what I've learnt by browsing meta and the help files, the main reason for this type of rejections is that it bumps the question to the front page, and overusing editing gives old questions attention at the expense of newer posts. But that's not really an issue here, is it? Edits suggested while reviewing new posts involve questions only a few minutes old.
There may be some problems with allowing retagging while reviewing. For example, there is possibly no indication in the review queue for suggested edits that it was suggested during reviewing, and therefore it might be hard to discern from a "normal" edit suggestion.
However, considering there are loads of mis-tagged questions, old and new, I think math.SE as a whole could benefit from allowing the minor edit of retagging during reviewing. I also suggest that the suggested edit reviewer should be informed if the edit was made during reviewing a new post or not. This would then indicate that a minor edit may be approved.