I have no idea if anyone else has discovered this. But there's a way to give special abilities during the game.
This requires no buildings to upgrade them and i happens imediatly. it also requires no killing of any sorta or extended players.
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This is how it works
xxxxxxThe ability has to be researched by the computer player.. And the computer needs the unit that uses that ability at the current time of the upgrade.
xxxxxxThis unit can be created at any time during the game, and can follow any conditions, in my testing map it's triggered by killing a powerup.
xxxxxxOnce it is time, create the unit and give it to the human player, you may then kill the unit or leave it as is.
xxxxxxThe human now has the special ability that the computer player had researchable. I have yet to test if this works with the abillity disabled, but it does work when it is enabled for the human player. (does not mean researched).
Here's the example map. Let me know if this has been done. (also know that upgrades do not work, i was just testing them).