Section 6-609. Procedure to register child support order of another state for modification. A party or support enforcement agency seeking to modify, or to modify and enforce, a child support order issued in another state shall register that order in the commonwealth in the same manner provided in Part 1 of this article if the order has not been registered. A petition for modification may be filed at the same time as a request for registration, or later. The pleading must specify the grounds for modification.