I usually have mine on auto which sets the MTU at 1500. Had to manually set it at 1200 due to downloading windows 10 this morning. It sucked plain and simple. Changed back to 1500 when my download was done and things started to improve a little.
I tried setting it lower to see what people were taking about and I kept getting a bee error. Went back to the auto setting after that. Unfortunately I don't think there is anything that bungie can do about it because it's not a hack, but an actual manual configuration of your internet connection. The best they could do is set a required MTU to be able to play.
Doing what you did is understandable. Network manipulation can be tracked though, and Bungie is already banning those who used it in Crucible. Done deal.
It's going to be tricky for them to prove it was actual manipulation though. It works for some, but not others and I believe it depends on your internet connection as well. Besides, they can't ban me from a game because I had to manually set up my home network to play their game. The real problem lies in the fact that there aren't any dedicated servers for the game in the first place.