It is possible:
When you cast the spell, you remove the old spell and add another(with same tooltips/manacost etc, the only thing you change that it is based on some other ability like "taunt" and you add that ability larger cooldown(in object editor).
Than when the ability was cast and you remove it, you add this ability based on taunt and order unit to taunt (unit issue order with no target> night elves mountian taunt.
Than you wait (pooled wait) the cooldownd duration and remove taunt and add the old ability.
So you just need 2 abilities:
- first original
- second(fake one) just like the first one only thad does nothing and have bigger cooldown
- you swap them
And why do you need that anyway?