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 sections 6–601 to 6–608, inclusive, if the order has not been registered. A petition or comparable pleading for modification may be filed at the same time as a request for registration or later. The pleading must specify the grounds for modification.