An approved STC plan may be modified by the employer with the approval of the Commissioner. If the hours of work are increased or decreased substantially beyond the level in the original plan, or any other conditions are changed substantially, the Commissioner shall approve or disapprove such modifications. The expiration of the original plan shall not change. If the substantial modifications do not meet the requirements for approval, the Commissioner shall disallow that portion of the plan in writing as specified in subsection 1455(a) of this title. (Added 1985, No. 140 (Adj. Sess.), § 1.)