If you want to enable cheats right away so you can use them without completing career/tournament/knockout/hot pursuit modes, do the following:
- Open your config.dat with a hex editor (like FrHed)
- Go to offset 0xc04 and change it from 00 to 01
(https://imgur.com/e7soU3c.png) - Save the file. Now you can use cheats in NFSHS!