There aren't real cheats but there are unlockables and secrets.
Unlockables[]
In order to get the Credits Theme, a player would need to Beat the game.
In order to get Razor Burn, a player would need to get 24 license plates.
In order to unlock Combat Mode, a player would need to get 12 license plates.
Secrets[]
In order to get Moogoo Monkey for the casino, a player would need to play The Sims 2 (Nintendo DS) with The Sims 2 (Game Boy Advance) in the GBA slot. This is unavailable in the Nintendo DSi, DSi XL, 3DS, 3DS XL, 2DS, New 3DS, New 3DS XL and the New 2DS XL because it does not have a GBA slot but instead you can play Moogoo Monkey on wireless until you're informed you got it. It is possible to unlock Moogoo Monkey in The Sims 2 by using a DS or DS Lite and then playing it on a DSi/DSi XL/3DS/3DS XL/2DS/New 3DS/New 3DS XL and New 2DS XL after the game is unlocked.
Another way to get Moogoo Monkey for the casino, is to play the game on December 14.
When you unlock the Bovine Shrine, there will be three other Sims worshipping The Prime Heifer with Ava Cadavra. These Sims are Ara Fusilli, Auda Sherif, and Sancho Paco Panza. You cannot interact with these sims as they are in a trance.
Each NPC has a secret that they will only share with your sim when they fully trust them.
Secret outfits become unlocked when your Sim visits the start panel after completing the game