The document itself is not required by law. The constitution simply states that the bank and the owner must "agree to the value." But the issue is not that basic and simple and the constituion doesn't specify exactly HOW the agreement is to be documented.
You won't get "cited" for not having this document in file (unless by internal auditors). But if you don't have the document in file, you'll run into problems during foreclosure as your lien might be ruled invalid.
I agree with Randy. You need legal counsel advice, as Texas homestead lending is quite tricky.
The more you sweat in training, the less you bleed in battle.......