JAR Ops 1.255 ii (e) specifically allows for the Commander to upload any extra fuel in addition to the standard required components that he/she deems necessary for the safe completion of the flight.
So at Ryanair, one must play them at their own game.
The question to the anonymous author of the memo must be "Are you seeking to prevent me from taking action which I believe necessary for the safe conduct of my flight?"
We live in an age of profligate litigation, precisely because companies like Ryanair chose to uphold, not the spirit of the law, but the letter.
Bankers/Google/Amazon have tried to use this type of defence recently but the tide of public opinion suggests people are tiring of it, rightly so, IMO.
Utterly contemptible in such a safety critical industry.