Voiding the warranty isn’t inevitable for DIY repairs. Framework legitimately seems to support self-repair and third-party repair, and I think nrp tries to make the warranty situation clear in what he says (note nrp, the person posting this, is Framework’s founder):
In other words, if you damage the mainboard by your rework, they’re not going to cover that under the warranty, but that doesn’t mean the warranty is void. If you implement the fix, and, for example, your keyboard stops working some time later, or you have problems with one of the known defects (fraying USB cable, loosening hinge, etc), the warranty will still cover those.
This is as warranties should be: simply repairing or modifying the device shouldn’t void the warranty, it should just mean that self-inflicted damage isn’t covered. That is, of course, somewhat up to the interpretation of the company, but that’s also what companies can build reputations on.