WEll, if it were me I'd dispute the whole ticket charge, not just the $6... since CO won't see that.. the issue has far more to do with CO's can't do culture than anything else.
They don't empower their people to rebook people, they don't empower them to comp drinks (in fact they make them enter in the cert #s for thsoe drinkie chits as if a 50c bottle of booze is a bottle of oxy..), they let them push FREE for the whole plane but they better be prepared to face the consequences of $quandering CO's money.
What would be the harm in giving the pursers a "credit card" that actuates a screen?