This should prove to be interesting--I got quite different info from the OnePass service center last week (for instance, the $50 redeposit fee is only for non-elite members). See http://www.flyertalk.com/forum/Forum20/HTML/006860.html for what they emailed me.

If you think about it though, what the agent told you makes absolutely no sense, since if you needed to change something on the itinerary, you might as well just redeposit the miles and issue a new reward ticket (since it would only cost you $50 to redeposit, rather than the $100 to change). I don't see how it would make any difference from an availability standpoint whether its a ticket reissue or just a new issue...