Skillchange abilitiy

Hey guys! I have been working on a map rcently and i tried to make a special hero. He is basicly a upport with stun, self invul a healing ray and healing totem, but his absolute ability would be that he shifts into twilight to become a powerful damaging wizard. Now changing the hero abilities were problematic for me, as simply making them to unlearn with a trigger just throws them back to the learning tab, so i tried the "Upgrade" with engineering. It seemed fine, but the abilities are messed up.instead of the invul i wanted a mana drain ability, but now he just turns invul forever and so on.
So I figured that there is no way to skillchange with engineering update. Anyone knows a way how to change the skillset completely on a hero? then reactivating the ability he would retain all of his former stuff.

You can give the hero all the abilities (both normal as well as the transformed abilities) in the object editor.
Then, when a player selects that hero, disable all Wizard-abilities like this:

• Player - Disable [Ability] for [Player]

When the hero transforms into a powerful wizard, disable all his regular abilities and enable the other ones.
When transformation is over, re-enable is normal abilities and disable the other ones.