Didn't overriding Catnip use to give 4 legs the first time. I could be misremembering but I thought overriding gave a taur body on the first use. Now it takes 2 and overriding the first time doesn't change anything from using normally.
Normally, the menu prevents you from using Catnip on a body part that is already Feline. 'Override' lets you use it on certain already Feline parts for extra effects. It does not force the 'overdose' effects on non-Feline parts.