Is filing a claim the only way to access common law?
In simple terms, No. Common law may be evoked at any time, in any case. However your position is stronger when operating under YOUR own claim/ case as a “prosecutor”/plaintiff vs as a “defendant” in their case. The key is, the prosecutors states the law (rules) of the case. Defendants therefore have little standing. Your goal would be to turn their case into your claim/ case. The law of the case if YOURS to write then. the Plaintiff has a huge advantage.
Where the matter in controversy exceeds $20, common law may be evoked by way of the 7th Amendment to the Bill of Rights which constrains the Government. You have a right to a trial by Jury, not just an administrative hearing, where you are considered merely a “citizen” or “person”, not a living man or woman, with no real rights. The prosecutor/ plaintiff will push you into their jurisdiction, if you are not careful.
It can also be evoked by way of the Amendment 9 constraints, which guarantees a man access to the King James Version of the law, such as claiming the right to face his accuser. (Acts 25:16).
The 9th Amendment to the United States Constitution, is the open gate by which a man may claim all rights antecedent to the Constitution. But if you don’t make YOUR claim, you won’t get remedy in common law, and most attorneys cannot go use this form of common law rules. Only YOU have that much authority as the living man.