Individual Unit Upgrades. Help!

[:1]How do I make multiple units have the same upgrade but when a unit does the upgrade, he is the only one that gets the effect. Then another unit of the same type can do the upgrade too and get the same effect, without all units getting the effect when one unit does the upgrade?|||make a no target dummy ability and delete all its functions and give it to a unit.. and then make a trigger that when to ability is used it will replace the unit who is using the ability with another..