The flesh remains under the Law.
What grace does is make the Law internal, instead of external. If Christ is the Law for your flesh, then when spirit and Spirit are merged in your soul, the Law for you is internal. Your heart subjected to Christ as Lord delights in righteousness. You learn that obedience is relief from all kinds of oppressing evil.
The Law living in your soul is much harder than the Law applied externally. That’s because the Living Law awakens your convictions. Instead of a broad generality in words of command, your convictions are specific to you alone. It covers a host of things the Law in words cannot address.
Thus, you leave behind the Code of Moses/Noah as you rise to a much higher standard. That standard does not — cannot — transgress the written Code, because the written Code descends from the standard of the Spirit. The written Code is merely an expression of the Spirit. It’s all one thing.
What’s left for you in Romans 6 is to unleash that Living Law to compel obedience on the flesh. Your conscious awareness has the choice to move from the flesh into the heart, the place inside of you that connects flesh and spirit. The wiring is already there; just start sending signals through it.
Yes, the flesh will rebel, but like all things organic and physical, it can be trained to obey as long as the heart and spirit are watching. It can become accustomed to what the heart knows from the grace of God. The longer you do strive for this, the more obedient the flesh becomes, in that it is overwhelmed by grace. We use the Code of Law to help us keep the flesh in line, to ensure we have fully embraced the Covenant.
Which Law restrains your flesh? The written Code has no power of its own. It requires someone to enforce it. The quality of that enforcement depends on whether the enforcer/ruler is led by the Spirit or by his own best estimate of the written Code. As long as someone involved in government can speak from the Spirit, it could in theory work well enough. Though as we see from the history of Israel, it typically doesn’t work too well. Still, there were golden moments in that history when things went rather well.
But if you are ruled from the Spirit/spirit nexus through your heart, then you don’t need government. It’s still there, but you don’t take it too seriously, because you are driven by a much higher moral standard. You have become the Law in that Christ lives in you.
The only question is which Law has jurisdiction over your flesh.