OP was not likely entitled to the free change because the fare bucket availability is unknown. Not suggesting that there are not agents who waive all manner of fare rules. Just not this one.
The OP's conduct is pretty shocking and his having earned "SSSS" is somewhere between an intentional act of the agent to karma to random with the latter being the most likely. As OP ought to know, "SSSS" on itnernational departures to the US is much more prevalent and the carrier is much more involved than on domestic tickets.
Whether the agent did this to OP or not, his conduct both in the past and in the moment is pretty shocking. It was wrong not to provide the EC 261/2004 information to his travel companions on his earlier travel and it was doubly wrong to threaten the agent with what is close enough to extortion, e.g. "if you don't break the rules for me, I will cost your employer money."
Whatever the outcome of OP's request, it never, never, never pays to engage in policy debates with people who don't make policy. Anybody sitting at a counter does not make policy.