When the amount of any unusual item includible in the income, operating revenue, or operating expense accounts is relatively so large that its inclusion in the accounts for the year in which the transactions occurred, would seriously distort net income, the company may request permission to include all or a part of the amount in account 186, miscellaneous deferred debits, or account 253, other deferred credits to be amortized over such period and through such accounts as the commission shall determine. Without permission of this commission, no such item shall be carried beyond the calendar year in which the transaction occurred.