Two answers here have involved tweaks to Mass Effect 3's ini files, and in particular Coalesced.bin. I've seen some unsubstantiated rumors that EA will ban players who use a tweaked .bin file in multiplayer, since they could potentially use it to cheat.
I don't want to test this out myself to see if I end up banned, as I happen to enjoy multiplayer. Is there any official word from EA (or firsthand experience) that if I implement a tweak such as the FOV tweak, I will be banned if I forget to revert back to the original file before playing multiplayer?