CompMetamorphosis is a comp class that makes an animal turn into a different animal after a given time. Only faction is preserved after the change, losing all possible hediffs (both negative and positive), training and family relations.

    //A comp class that makes an animal change into another animal after a given time

    public float timeInYears;
    public string pawnToTurnInto;
    public string reportString = "VEF_TimeToMetamorphosis";

It is a comp class, so you just add it in XML in the <comps> tag. For example, this allows the Angel Moth Larva to turn into adult Angel Moths in Alpha Animals

<comps>
	<li Class="AnimalBehaviours.CompProperties_Metamorphosis">
		<timeInYears>0.4</timeInYears>
		<pawnToTurnInto>AA_AngelMoth</pawnToTurnInto>
	</li>
</comps>