Registering a custody/child support order

Is there a waiting period between registering an order and filing to request a change of venue?
Are there specific forms to request a modificaiton?
Can you request a change of venue and modification of child support and custody at the same time?

A order is registered in the county where you reside and then enforceable state wide. Venue referes to different counties were actions are set, not where orders are registered.
I suggest you file a motion to change venue prior to filing a motion to modify.

It is an out of state order. Can the order get registered and a request to change venue be done at the same time or is there a waiting period between?

You would just register the order in the county in which you live. If you wish for NC to have jurisdiction you will need to file a motion to have the issuing state release jurisdicion.