Save Corruption: The #1 risk. If the editor doesn’t properly "resign" the save, your Xbox will see it as a corrupt profile. Always keep a vanilla backup on another USB drive.
Online Bans: The Xbox 360 servers for FH1 are mostly offline, but if you use a modded save and then play a title that shares anti-cheat (like later Forza games on Xbox One), Microsoft could flag your profile. For FH1 alone, bans are extremely rare.
Achievements Glitching: Some achievements (like "Gotta Have 'Em All" for collecting all cars) may not pop if you unlock them via editor. They might require one more legitimate in-game action to trigger.
DUPLICATE CAR GLITCH: Some older editors accidentally give you 255 copies of one car instead of one of each. Use a modern, trusted editor.