§ 223. Modification of board decisions or orders. Upon its own motion or upon the application of any party in interest, the board may at any time review any decision or order regarding disability benefits and, on such review, may make a decision ending, diminishing or increasing the disability benefits previously ordered, and shall state the reason therefor. Upon the filing of such decision regarding disability benefits, the chair shall send to each of the parties a copy thereof. No such review shall affect any previous decision as regards any moneys regarding disability benefits already paid, except that a decision increasing the disability benefit rate may be made effective from date of commencement of disability, and except that, if any part of the disability benefits due is unpaid, a decision decreasing the disability benefit rate may be made effective from the commencement of disability, and any payments made prior thereto in excess of such decreased rate shall be deducted from future disability benefits in such manner and by such method as may be determined by the board.