ak-73 said:
No, they cannot. You did not read my advice and check out page 219 in its entirety.
"He only needs to spend this cost once, however, and once an ability has been activated, it remains so for the remainder of the Mission (if the ability is Sustained) or for the duration of a single combat (if the ability is not Sustained)..."
Beyond that sayles78 is right: a specific descrription overturns a general rule.
Alex
What about if you change to a different power and want to go back? You have to repay the cost or, since you already paid, it's free?
I admit that I missed the once per mission cost statement. That implies you might as well just spend all your cohesion immediately so you don't lose it due to damage, then swap modes as needed (it would make rejoining Squad mode during combat a pain).