The changes would apply to the current bike you are actually selecting. You may however just code the button the way the overlord buttons are coded, select all of them and upgrade. This is triggered by the OK_FOR_MULTI_SELECT option in the CommandButton.
If you want a global upgrade add a commandset change to the Arms Dealer or add an global upgrade to an "alive" back, as you said, that is then a PLAYER type upgrade, not an OBJECT type upgrade.
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