(9) Notice of Participation in an Appeal. Within 21 days after an appeal from a Commission order has been docketed as provided in subparagraph (8), any party to the Commission proceeding who did not file a notice of appeal may file a notice of participation with the clerk of this Court. The notice must identify whether the party seeks to be an appellant or appellee. If there is more than one appellant, the notice of participation as an appellant must identify the specific appellant(s) with which the participating appellant will align. Participating parties must follow the briefing schedule and requirements of subparagraph 10, except that a participating party may not raise any additional assignments of error or cross-error. The notice of participation as appellant or appellee must be mailed or delivered to every other party to the Commission proceeding. Every party who has not filed a notice of appeal or notice of participation, or having filed a notice of appeal does not file a petition as provided herein, will not be a party to the appeal and no further papers need be served on such party. Notwithstanding the foregoing provision, a necessary party who does not file a notice of appeal, petition or notice of participation is deemed an appellee. The Commission need not file a notice of participation and will be deemed an appellee.