Looking for a mod to disable gain and loss of fat and muscle

Would the fit/fat limits in MC CAS turn it off for all sims in the save file? Also, does it only make the fit/fat sliders to not move, not set them to some kind of standard value?

And another thing, I have never used MCCC, it seems a bit overwhelming tbh ^^' If I install MCCC, will all the settings be at standard values of how the game works without mods, or will I need to change anything to make the game work just as how it works without mods except for the specific changes I make (fit/fat settings)?