That's like saying "I am five foot tall" stops being true when you use a different definition of "tall" (switch it to weight, for example). This isn't insightfu

That's like saying "I am five foot tall" stops being true when you use a different definition of "tall" (switch it to weight, for example). This isn't insightful and it's also false. People have agreed on how the plus sign should be defined when it comes to adding two integers, and they've agreed on how to write integers, in which case 2+2 is always four. The only way to change that is to change the meaning of at least one of the four symbols "2", "4", "=", or "+" to some private meaning which no one else shares -- e.g. to distort the language in order to sow confusion, which the use of agreed upon meanings for symbols is designed to eliminate. Moreover this idea that a sentence changes its truth value the moment someone changes the meaning of one of the words in the sentence is not some deep statement or interesting observation, it's just pointing out that language is useful only if people agree on the meaning of the words.