Section 31.05 - Intervention(1)Substitution of Parties. An agency may, on motion, at any time in the course of any proceeding, permit such substitution of parties as justice or convenience may require.(2)Intervention. Any party not initially joined in the action or proceeding shall be permitted to intervene. In the discretion of the agency, any person not a party may be permitted to intervene in any action or proceeding. A person or party desiring to intervene shall file a motion in accordance with 950 CMR 31.03(6), which motion shall state therein the grounds for intervention.