Tex. Tax Code § 11.424
To the extent of a conflict between a provision in a contract entered into by an organization, association, or entity with the United States and a provision in the charter, a bylaw, or other regulation adopted by the organization or entity to govern its affairs in compliance with Section 11.18(f)(2), 11.19(d)(5), 11.20(c)(4), or 11.21(d)(5), the existence of the contract or the organization's compliance with the contract does not affect the eligibility of the organization, association, or entity to receive an exemption under the applicable section of this code, and the organization, association, or entity may comply with the provision in the contract instead of the conflicting provision in the charter, bylaw, or other regulation.
Tex. Tax Code § 11.424