Is it supposed to be a passive skill or an active? That may help.
Why didn't Endurance/Devotion work? What exactly is it supposed to do that they could not fulfill?
Inner Fire adds armor (I believe)
Yes in the object editor, as an upgrade (I think there is an 'Upgrade' tab) create one that does absolutely nothing and give it to the tower you want to sell.
Also, don't double post, simply edit your previous post.
I would say have a trigger than fires when the ability is cast. Then pick every unit with that specific buff and turn them invulnerable, wait some formula of time (To solve the problem you mentioned in the above helper's post, just have it wait like (X * Level of Ability) seconds), then remove it.
Create a research upgrade called "Sell Tower" or something along those lines, and then have a trigger with the event of Research Completed or something along those lines (Sorry I don't have WE open right now), destroy the building and give X gold to owner of the tower.
I am pretty sure, unless you change the color values. Although because it becomes more transparent it would be harder to see the colors, but they would be there.
It would make the trigger easier to read and interpret. Thus causing less confusion.
It turns:
Ouch
Events
Map initialization
Conditions
Actions
If (All Conditions are True) then do (Then Actions) else do (Else Actions)
If - Conditions...
Well, 0% Transparency makes then visible, 100% Transparency makes them totally invisible. I would say just mess around a bit with that number until you find one that is suitable.