Upon its own initiative or upon the application of any party in interest on the ground of a change in conditions or because of a mistake in a determination of fact, the commission may, at any time prior to one (1) year after date of the last payment of compensation, whether or not a compensation order has been issued, or at any time prior to one (1) year after the rejection of a claim, review a compensation case, issue a new compensation order which may terminate, continue, reinstate, increase, or decrease such compensation, or award compensation. Such new order shall not affect any compensation previously paid, except that an award increasing the compensation rate may be made effective from the date of the injury; and if any part of the compensation due or to become due is unpaid, an award decreasing the compensation rate may be made effective from the date of the injury, and any payment made prior thereto in excess of such decreased rate shall be deducted from any unpaid compensation in such manner and by such method as may be determined by the commission.