30 Tex. Admin. Code § 295.71
An applicant for an amendment to a water use permit or certificate of adjudication shall file an application prepared in the manner of an original application for a permit. However, the title of the application should be altered to reflect the fact that it is a request for an amendment. A proposed amendment, including an amendment on the motion of the executive director, shall be recorded in the same manner as a permit application. The holder of a permit, certified filing, or certificate of adjudication issued before September 1, 2001, for industrial use or irrigation use where the actual use of the water is now classified as agricultural use may continue to use or supply water in accordance with the previously issued permit, certified filing, or certificate of adjudication without obtaining an amendment.
30 Tex. Admin. Code § 295.71