I went for the following :
-Network : Most of the stuff that are not usually considered cheating (by my standards at least), can be in Multiplayer. The simple fact that only the host can use the in game editor or the scout (w/e they are used for), is clearly a cheat
-Editor : for the editor(s) as well, not every use could be labelled cheating. I think it's fair (sometimes) to just max out your players' knowledge of your tactic, you don't wanna pay the price too hard for changing tactic mid season sometimes. On the same note, checking CA/PA in the pre-game editor is just the same as using the scout (less effective tho). BUT, changing attributes, constantly removing injuries, bans etc, can be considered cheating. In the same way, changing stuff on the pre-game editor to have an easier time is also some kind of cheat, obviously.
-Save/Reload : I think this speaks for itself :p unhappy with a loss ? reload. It's easy, it's tempting, but losing is part of the game, even when it's infuriating. Nobody likes to lose 1-0 in the CL finals when the opponent hasn't even made a single shot, but their cross at the 92min just happened to hit your defender on the head while he wasn't looking and it went in. But it's part of it. FM wouldn't be FM without the rage inducing gameplay.
-Add manager : Adding managers ingame to buy/sell players is probably the easiest way to cheat. You can get money and the team of your dreams this way, but, however you look at it, it is clearly a cheat to do so :p