There is some discussion below about this topic which you can read but... again short answer
If you want to play with "main game" (I understand you mean Party Mode). You need to create account in the game and MovieStats. By this after the game is finished your best movies will be exported to MovieStats. They will be then comparable with movies of other players. So statement that this is single player game and not affect other players is not exactly truth.
Solution. If you want to use cheat codes you can make donation on Bronze level. This will enable to you possibility to use cheat codes in Party game (but after using first cheat code which is related to cash export of the movies to MovieStats will be blocked so it will not affect Online BoxOffice in MovieStats).