I have something look around but I don't found something what let me think 'this could help me to oriental' (I hope I have used the correct word) ^^
What I am looking for is a guide to introduce in the CAS modding, but I don't want to create a Slider or add new Clothing. What I am missing in the game, with The Sims 3 Supernatural, is in the Supernatural Beeing list the mermaid and the PlantSim, if The Sims 3 University Life and The Sims 3 Island Paradies is installed.
I need something lead.
Would it be a 'simple' overwrite Mod or has to be it a Script Mod or something like that?

I know that Nraas master controller has this option to make a sim a supernatural, but for people who doesn't like Nraas or for whatever reason, your idea would be really great! I would be the first one downloading it Anyway, I guess since nobody actually did, it might be a hard one to do. I guess the way to do it might be inside the UI.package, though I might be wrong about that. I never really went to deep into script modding, but I am sure you can add more to it. Though, I guess for making it functioning, you need to do more than just tell the script 'hey I want my sim to be a plantsim.' And I guess because of the other EPs with a creature like that, you could easily mess up the game if someone doesn't have one of the EPs, like University Life. I guess this doesn't really help you out, but it's something to have in mind when you're going to publish it on the internet ^-^