Tex. Family Code § 156.102

(a) If a suit seeking to modify the designation of the person having the exclusive right to designate the primary residence of a child is filed not later than one year after the earlier of the date of the rendition of the order or the date of the signing of a mediated or collaborative law settlement agreement on which the order is based, the person filing the suit shall execute and attach an affidavit as provided by Subsection (b).

(b) The affidavit must contain, along with supporting facts, at least one of the following allegations:

(1) that the child's present environment may endanger the child's physical health or significantly impair the child's emotional development;

(2) that the person who has the exclusive right to designate the primary residence of the child is the person seeking or consenting to the modification and the modification is in the best interest of the child; or

(3) that the person who has the exclusive right to designate the primary residence of the child has voluntarily relinquished the primary care and possession of the child for at least six months and the modification is in the best interest of the child.

(c) The court shall deny the relief sought and refuse to schedule a hearing for modification under this section unless the court determines, on the basis of the affidavit, that facts adequate to support an allegation listed in Subsection (b) are stated in the affidavit. If the court determines that the facts stated are adequate to support an allegation, the court shall set a time and place for the hearing.

(d) Subsection (b)(3) does not apply to a person who has the exclusive right to designate the primary residence of the child and who has temporarily relinquished the primary care and possession of the child to another person during the conservator's military deployment, military mobilization, or temporary military duty, as those terms are defined by Section 153.701.