The Rules of Professional Conduct apply only to lawyers and are the foundation for a lawyer to be suspended from the practice of law or disbarred or receive other license related professional discipline. They are neither criminal offenses, nor on their own, a grounds for a civil lawsuit (although they may be relevant to an element of a civil cause of action giving rise to a lawsuit).
The Rules of Professional Conduct also prohibit using a non-lawyer as a sock puppet to violate the Rules of Professional Conduct.
But, the Rules of Professional Conduct themselves are not applicable to pro se parties or even to non-lawyer parties who are acting fully independently of the lawyers they have retained.
In some circumstances, a violation of Rule of Professional Conduct 3.4(g) could also constitute the crime of extortion, or could constitute duress such that an action taken in the course of litigation or a business deal is not actually legally considered to be voluntary and making it potentially voidable. But this would not always, or necessarily even usually, be the case.
Incidentally, Rule of Professional Conduct 3.4 is one of the Rules of Professional Conduct with the most state to state substantive variations and it also has multiple differing interpretations even in cases where the language is verbatim identical between states. The appropriate scope of this rule as a matter of policy is one of considerable controversy. And, it isn't unusual for the converse to happen (i.e. for a criminal prosecutor or an attorney regulation system official to force the hand of a civil litigant in the course of negotiations about those charges).