That mod is called Master Controller and Twallan is the creator.  MC does a multitude of things, one of which allows you to add to the Lifetime Happiness points which will then enable you to acquire the rewards.  Simmunity is a must for me   .

If you are going to use a cheat, why not use one to increase lifetime happiness points.  Then you can purchase the simmunity reward.  I use it all the time, because I was tired of all my sims getting sick.      I personally use the MC mod which enables that feature.  BTW, there is another request for this very same subject about a lifetime happiness reward cheat just below your post.

Nice house!!  Thank you.

very nice...thank you for sharing her!..

I used one like this is TS2 and loved it....I know this one will be just as well used....thank you! 

Great idea...I was getting tired of having to use the same old colors every time...thank you!!

I'm just beginning to discover the fun in gardening...your mods will be much appreciated and well used....thank you very much for sharing them. 

Great looking tree..thank you!!

It's adorable...thank you!

Very creative...love it!  Thank you for sharing.

Beautiful Bella.... ...thank you for sharing her.

Another enigma resolved....thank you for sharing!!

I could really use this....thank you for sharing!

I used a mod like this in TS2 and will definitely use it for TS3....thank you for sharing it.

You've made another handsome sim that I simply can't resist.  Thank you for sharing him.