A 14 tonne change is a large change. It will significantly change every figure on the fuel log - burn, contingency, FR & holding if required. It the flight was an EDTO flight, it will also significantly change the EDTO fuel calculations. While it is still possible manually work out the changes to most of these fuel figures or simply throw enough fuel on that there is way more than the required fuel on board, there will be no accurate breakdown of the various figures.
If the flight was in fact an EDTO flight, there is a requirement to have accurate diversion fuel figures to hand & most, if not all, manuals state that a computer flight plan is required to carry out the flight & that a new flight plan is required for significant changes.
There seems to be more going on here than what has been reported. I have noticed that these sort of reactions tend to happen when there has been some sort of 'history' with an individual & others are just waiting for the opportunity to get some 'payback'. Who knows what was going on here.
Whatever the situation here actually was, the lesson for everyone is to be very careful when trying to 'help' the company and/or the passengers out. It is often better to just ask for a new plan & cop the delay. If you don't make curfew, just do the divert & leave the mess to the company to sort out. Management love it when you make it work, but usually drop you like a sack of hot potatoes when it doesn't.