What's the chances of "disarming an officer" charge being lessened or dropped in a first offense?

It might depend on your attitude.  You made life difficult for a police sergeant who was just doing his job, so he's made your life difficult.  If your uncle has friends on the force, you might talk to him about whether apologizing to the sergeant for being a jerk, just man to man, might be a good idea.  And you need to give some thought to why you keep having trouble with cops, think about making some changes.

Police officers have a fair amount of leeway, under the law, in deciding what charges to file in a given situation.  And police officers are human beings, like the rest of us, they don't usually respond well to disrespect.  Whether you can get a plea bargain, and if so how good it will be, will probably depend at least in part on what the cops say to the prosecutor, when he asks about the case.