Add the forge SpecialSpawn event to the mob spawner spawning method (like vanilla does). This makes mob stats modifiable by other mods.

What do you mean by "modifiable"? If your intention is to enable powered spawners to spawn entities with the same NBT as the original, then the answer is no because that's OP.

Could be used to make mobs have more health the more the spawner spawns or something

^
example: my mod modifies the health of mobs and such during spawn.