You are not required to have an attorney for a child custody modification in New York. If you and the other parent are in agreement on the modification and there is no conflict, you may simply wish to go before the judge and have the new custody plan approved, although it can be important to have an attorney review the agreement to be sure it protects your rights and interests. But, if the other parent is opposing the modification requested, you stand a much better chance of gaining a favorable outcome with legal representation.