My success rate with getting ANY kinds of seats changed/chosen on DL.com is about 25%.

I book with an agency, and come back an hour or so later to DL.com after it is ticketed, and still fail. Maybe there's something wrong with my account.

I end up DMing @deltaassist with a PNR and a list of seats I'd like, and they take care of it, but it's a waste of my time (and theirs) to have to do it this way.