You basically already have a Constitution-esque "right to root", as changing the software on hardware you own is not illegal. What we're actually dealing with is technical measures that can effectively prevent us from doing so. There are a few legal hooks that augment the natural landscape (DMCA, contract terms, etc), but remove those and the problem would remain.
So unfortunately, what we're really looking for is some positive government regulations that would make companies have to publish some of their documentation and source code. That's much harder to create and draft, although for a simple first stab I would look at requiring that source code be available to make a work eligible for copyright protection.
I acknowledged the DMCA. The DMCA and other legal restrictions are indeed problems. Another one is likely emissions requirements, which at the very least discourage tractor owners from replacing the computers wholesale.
But even if these legal restrictions were to vanish tomorrow, we'd still be stuck with a similar landscape - most manufacturer control comes from technical restrictions combined with a high rate of churn so even if someone invests the time to figure something out, it quickly becomes yesterday's model. Fundamentally, understanding is more difficult than creation.
The calculus could be different on tractors, which are meant to last a real long time. Except the topic here too is focused on getting companies to positively supply things to help, rather than removing laws that hinder (FTA: "The agreement creates a mechanism to address farmers’ concerns and give them access to resources needed to repair their own equipment, such as diagnostic and repair codes, manuals and product guides.")
So my ultimate point is that you need to move past thinking that a Constitutional "right to repair" law would address these problems. Such a thing would be as ineffectual as the Constitutional "freedom of speech" has been in addressing the social media oligopoly.
Only if the DRM protects a copyrighted work, and even then only if the "protection" goes beyond protecting the software from being executed/used. (Chamberlain v. Skylink)
The DMCA doesn't really care about what you do after. The "DRM" has to directly protect a copyrighted work. By your logic, a CFAA violation is also a DMCA violation.
So unfortunately, what we're really looking for is some positive government regulations that would make companies have to publish some of their documentation and source code. That's much harder to create and draft, although for a simple first stab I would look at requiring that source code be available to make a work eligible for copyright protection.