This is a tricky one. Despite the enormous amount of manuscripts and proposals we go through, and despite delegating interns and assistants to deal with the slush pile, you’d be surprised how many queries an editor or agent can remember. I almost always notice a re-query (good word, by the way).
Personally, I prefer for the author to admit that they are re-querying me, but to do so towards the end of their query letter. That way I don’t have the uneasy feeling that someone’s trying to fool me into reading a pitch I’ve read before. Also, it’s just good to be honest.
As I’ve said before, I’m willing to seriously reconsider a query when the manuscript in question has been seriously revised. Like, revised to the point where I don’t get that “Hey, I feel like I’ve read this before…” feeling.
But better than re-querying is querying the right editor/agent with the right book and query letter the first time around. And if there’s one thing I’ve tried to pound into your collective head since the beginning, it’s the importance of doing your bloody research.
Good luck with your re-querying!