In the rule “Stables”, replace “Once every 72 hours, a Wizard may mutate a creature in another wizard’s stable and add the resulting creature to the stable of the wizard who mutated the creature.” with:-

A Wizard may mutate a Creature in another Wizard’s Stable by spending an amount of Food equal to that Creature’s Upkeep; the resulting Creature is added to the mutator’s own Stable.

For each Wizard, if the total Upkeep of Creatures in their Stable minus the number of Creatures in their Stable is greater than zero, reduce their Food by that amount (to a minimum of zero).