Add a new token to the [ANIMAL] token set.
[PET_VALUE_ALWAYS:value] would set the PET_VALUE for a creature within the given entity.
Why would this be useful?
It would allow for tailoring embark costs for entities, helping giving a very distinct feel of how the early game is on different entities.
Kobolds could have easier time with lizards, humans with horses (useful for when we will have fortress mode mounts for the player).
Conversely, it would be a way to make it more difficult for the player to access some of the creatures they could.
Also, it would allow to have creatures without PET_VALUE stated - say Trolls with the vanilla Goblins - to be paid a fair amount at embark without touching the creature raws. This would be useful both for mod compatibility and for mod maintainance along time, keeping up with different evolving versions of the raws.
The downside? Possibly the same effect could be "sort of" achieved "just" by altering the creature raws for each and every creature own [PET_VALUE] in its raws - that would make them the same for each and every entity to use, and would complicate mixing mods, having altered vanilla files to cohordinate.
Possibly, having different PET_VALUES for the same creature could create potential problems to merchant caravans from other enitites - maybe that would crash to desktop, I don't know. If it doesn't, having different values for something from different merchants would actually be an incentive to trade!
ALTERNATIVE OPTION. Having an [ANIMAL_EMBARK_VALUE:value] token would accomplish most of what the other solution does without changing the creature pet value in game. That would leave the effect on the creature adopting the pet flat for any species and it would solve the merchant potential problem.