I'm looking to update Synthmeat with a small moral penalty to show that its really not really a full replacement for meat. Kind of like a much reduced version of the penalty for eating human flesh.
My thing is since humanoid meat isn't a full entry I don't know how to reverse engineer it.
Under each ThingDef you'll find a <food> tag. This contains properties related to something being food.
Under there are
<eatenDirectThought> = the thought a pawn gets when eating this item.
<eatenAsIngredientThought> = the thought a pawn gets when eating a meal which has this item as an ingredient.
So just place those in, filled with the defNames of the thoughts you want to give.