(a) Except as provided by Subsection (b), a petition may not be supplemented, modified, or amended on or after the date it is received by the authority with whom it is required to be filed unless expressly authorized by law.
(b) If a petition is required to be filed by a specified deadline, the petitioner may file one supplementary petition by that deadline if the original petition contains a number of signatures that exceeds the required minimum number by 10 percent or more and is received by the authority with whom it is required to be filed not later than the 10th day before the date of the deadline. The authority shall notify the petitioner as to the sufficiency of the petition not later than the fifth regular business day after the date of its receipt.