No, it isn't okay. It's never okay unless you state in your query that you did submit before, and hope the agent will take another look after the major rewrite.
Agents do not have to remember you, and it probably won't be an intern who reads your query. Either way, unless the agent in question actually requested and read your manuscript, all the rewriting in the world isn't going to change her mind about your query. She doesn't know how good or bad the novel was before the rewrite, so why would a rewrite matter?
But the main thing is that it's simply annoying as hell when writers won't take no for an answer, and those thousands of other queries and partials and fulls coming in all mean there isn't time to chew the same food twice.
Re-query, if you must, but don't even think about trying to slip a re-query past an intern, or an agent. Most agents do keep track of queries and submissions, and the few who don't usually have very good memories. Be open and honest. Too many want to start a relationship with a lie, and this is always a horrible idea.
