These are questions with legal answers that depend upon the contract law and consumer law of a particular jurisdiction.
For instance, if a particular jurisdiction has a law that precludes the exclusion of certain statute-implied terms; or has a law that prohibits the inclusion of a certain term in a contract; then no one can agree to such a thing regardless of what they sign or what button they push.
A simple example that would apply in most jurisdictions is that no one can agree to sell themself into slavery, regardless of what document they might execute.
Anyway, I don't see that these legal examples shed much light on understanding the social process of converging on rules for RPGing.