Tex. Util. Code § 40.104

Nothing in this subtitle may impair the tax-exempt status of municipalities, electric cooperatives, or river authorities, nor shall anything in this subtitle compel any municipality, electric cooperative, or river authority to use its facilities in a manner that violates any contractual provisions, bond covenants, or other restrictions applicable to facilities financed by tax-exempt debt. Notwithstanding any other provision of law, the decision to participate in customer choice by the adoption of a resolution in accordance with Section 40.051(b) is irrevocable.