If you are in the military and are scheduled for deployment, it is natural to wonder if you need to go through legal channels to change your custody order. The best person to ask about your particular situation is your lawyer.
In general, it can be wise to ask a temporary custody order, but you do not necessarily have to.
Custody cannot be permanently changed because of deployment itself but...
Courts cannot permanently change custody because of deployment. However, a temporary custody order is an opportunity for you to set up legal channels for people such as your parents or spouse to visit your children while they are with their other parent. It can also address matters of child support and how often you get to communicate with the children while you are deployed.
If your co-parent is not suited for custody
In deployment cases, courts prefer that the children live with their other parent if it is in their best interests. If you do not want your children living with their mother or father for safety reasons or other legitimate reasons, a temporary custody order helps. The order would establish that the children are legally living with their grandparent, aunt, uncle or your friend, whomever the person is. The other parent would probably not be able to successfully petition for temporary custody once you are away or swoop in and disrupt the children's lives by taking them away from the person they are living with.
If a push for custody would be likely upon your return
If you feel that your co-parent is someone who will fight for custody once you are back, a temporary order can put certain protections in place. For example, it shows that the change truly was only temporary and that you went through legal channels to cross your t's and dot your i's.
For peace of mind
Peace of mind is worth a lot. So, you may want to do a temporary custody order even if everything seems great just to give you security.