I have Extremis Upgrade equipped to Punisher. Punisher stuns an opposing character in combat. Can I KO Extremis Upgrade to prevent Punisher from stunning and still get Punisher's KO effect on the opposing character?

No, Punisher's effect is a double check triggered effect, (as denoted by the "triggering event [comma] conditional clause [comma] effect" formating) the conditional clause must be true on both triggering of and resolution of the effect.

Not a double-check, actually---those all have "if" phrases set off by commas, in between the triggering event and the rest of the effect. Punisher's "while" phrase is more like an additional trigger condition, like Witchfire has; it's something that has to be true to trigger.

The answer comes from what kind of triggering event Punisher uses. His power is triggered off of characters becoming stunned---which means you look to the moment right before the event to determine whether or not he triggers. Even if you use Extremis Upgrade, he still had that equipment in the moment immediately before the triggering event, since mutual combat stuns are simultaneous.

crap, I saw the two commas offsetting a statement and got excited.

My bad.

Oh, wow, so it does work? Sweet.