Not only have I done it multiple times but I've also had the DM line re-seat my mother on a few flights where there were only middle seats in the back and she ended up either window or aisle much closer to the front.

Again, it all depends on the agent you get. If you don't like what you hear, be polite, hang up and call again and hopefully you get a different person.

There's a few ladies in SLC that I've had the pleasure of getting on the phone the last couple times I've called - not only can they pronounce my last name correctly - and it is a real bugger - but they've done wonders for me. There's one agent in particular who I always hope to get. I don't want to give her name out here for fear of something happening against her but I swear she is a magician of some sort.