Unfortunately, changing the text on your end has no legal effect. It's not a contract unless the other party agrees to your change.
When there's a EULA or similar, the company is trying to form a contract with you, usually with lots of unfair terms.
If replacing the text with your own and clicking a button that you renamed from Agree to Disagree voids the whole thing, well, mission accomplished.
There would only be a problem if the law says that not only does your modification not form a contract, but that you acted in such bad faith that you actually still somehow agreed to the original contract.