Bouncing

I want to be able to turn bouncing attack on/off
but tech items cannot be unlearned, any ideas?

I don't know if it works, but you could create a dummy ability (probably based on immolation with 0 mana draining) that adds and removes a spellbook with the bouncing abililty.

Nope, removing or even disabling ability has absolutely no effect,
bounce is still there.

I guess blizzard simply did not make it reversible.

What about a neutral ally with full shared control? Changing the owner of the unit might do it if the tech doesn't transfer.