So basically you can hack the necromancer interaction to transform people into whatever you want. I use this all the time and want to tell people about it. Here's how you do it.
Step 1: Create a creature
Do as you normally do with one exception. No color descriptors, because the game crashes when you examine a transformed creature with color descriptors. You gotta put that in the manual description, just type out their hair color, skin color, ect. Yes this does mean they'll all have the same colors to them unless you make a bunch of castes, no helping it.
Step 2: create an interaction.
For this example, I'll show the interaction I used to turn humans into Aristocrats (name subject to change) genetically engineered superhumans who rule over everything. Note that living beings can only permanently transform once. You can not make a creature you have turned into something turn into something else.
Some things to note:
I did not include a sphere for this secret. That means that unlike necromancy, which only gods of death can bestow the secrets of, any god can bestow this one. You can add spheres for your own if you like.
I made it so that only humans can become aristocrats, but of course you can modify it to work however you like.
[INTERACTION:GOD_SECRET]
[I_SOURCE:SECRET]
[IS_NAME:the secrets of becoming a god among men]
[IS_SECRET_GOAL:IMMORTALITY]
[IS_SECRET:SUPERNATURAL_LEARNING_POSSIBLE]
[IS_SECRET:MUNDANE_RESEARCH_POSSIBLE]
[IS_SECRET:MUNDANE_TEACHING_POSSIBLE]
[IS_SECRET:MUNDANE_RECORDING_POSSIBLE:objects/text/book_instruction.txt:objects/text/secret_death.txt]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:MORTAL]
[IT_REQUIRES:CAN_LEARN]
[IT_REQUIRES:CAN_SPEAK]
[IT_AFFECTED_CREATURE:HUMAN:ALL]
[IT_CANNOT_HAVE_SYNDROME_CLASS:WERECURSE]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYNDROME][SYN_CLASS:WERECURSE]
[SYN_AFFECTED_CREATURE:HUMAN:FEMALE]
[CE_BODY_TRANSFORMATION:PROB:100:START:0:ABRUPT_START]
[CE:CREATURE:ARISTOCRAT:FEMALE]
[SYNDROME][SYN_CLASS:WERECURSE]
[SYN_AFFECTED_CREATURE:HUMAN:MALE]
[CE_BODY_TRANSFORMATION:PROB:100:START:0:ABRUPT_START]
[CE:CREATURE:ARISTOCRAT:MALE]
Step 3: Optionally make them always be rulers
Basically you add [CREATURE_CLASS:whatever] to the creature, and then in the civ that the race which transforms lives in, you add [ALLOWED_CLASS:whatever] to all the positions you want to add it to.
What this will do is that transformed creatures, Aristocrats in this case, will ALWAYS be prioritized for being promoted to those positions. For example, doing this to the king position means Aristocrats would always be kings if there are any in the civ, or at least are much more likely to be promoted to that position.
But what is super interesting about this trick is the fact that these new creatures can reproduce. Obviously the first way is for two of the transformed humans to meet and marry each other. BUT if a female transforms into a new creature AND is already married to someone in worldgen, she will produce children of HER race even though the father is of a different race, which is obviously really handy in spreading the species around.
So yeah you can probably use this to make all kinds of cool things like clans of vampire overlords or dragon kings and stuff.