The place for mom to start is by seeing if her ex- will agree to her relocation. If he will, she can petition for modification of the custody order based upon his consent. If he will not, then she can petition with knowledge that she'll have to overcome his objection.
If he objects, one strategy would be to schedule the hearing on her petition for a date after your wedding but before you enlist, with your wife petitioning the court to lift the geographic restriction from the judgment to allow relocation after you enlist and relocate. You can enlist first, but as others have pointed out that can create problems for you if the petition is denied. She could petition with the hearing date scheduled before the wedding, but if the court senses that you and she may call off the wedding if she's not allowed to move you may cause the court to question the seriousness of your relationship.
If you have already enlisted, then you have little choice but to proceed and that the court sees things your (future) wife's way -- but you will be far from the first case that has come before that court where a parent sought to relocate due to a spouse's employment or military deployment.
That type of statement is frequently made, but is in fact a possibility that should be considered, not the certainty that some people suggest. It can be a negotiating point or an offer that may be made in court, if the parents creating the distance want to make the offer to cover all costs and are certain that it won't create economic hardship.
Modifying child support from the state formula is not as easy as that. Besides, if it all comes out in the wash, it makes more sense to keep the child support and let the court make a determination on the division travel costs. However, as this recent memorandum opinion suggests, it may be possible to convince a court to go along with a plan to modify or terminate child support in association with a requirement that parents share long-distance travel costs.
Nor do I.
I don't see a need for a parent to offer visitation beyond what is typical in a long-distance parenting plan; but if that's acceptable to the mother and allows her to get the father's consent without having to go to court, it's an option.
The general rule for modification of custody is set forth by statute:
Decisions on a parent's petition to relocate are made on a case-by-case basis, consistent with the best interest of the children and . A non-exhaustive list of factors that a Texas court will consider when evaluating a petition to relocate include:
Quoting Texas Family Code, Sec. Sec. 156.101. Grounds for Modification of an Order Establishing Conservatorship or Possession or Access
(i) the parents' good-faith reasons for and against the proposed move;
(ii) a comparison of economic, educational, health, and leisure opportunities for the custodial parent and the child;
(iii) whether the child's special needs or talents can be accommodated;
(iv) the effect on the child's extended family relationships;
(v) the effect the move would have on the noncustodial parent's visitation and communication and his ability to maintain a full and continuous relationship with the child;
(vi) whether the noncustodial parent has the ability to relocate; and
(vii) whether a visitation schedule could be arranged that would allow the noncustodial parent to continue a meaningful relationship with the child.