The parties, by agreement and with approval of an arbitrator or the Commission, may enter into a compromise lump sum settlement in either permanent total or permanent partial disability cases which prorates the lump sum settlement over the life expectancy of the injured worker. When such an agreement has been approved, neither the weekly compensation rate paid throughout the case nor the maximum statutory weekly rate applicable to the injury shall apply. No compensation rate shall exceed the maximum statutory weekly rate as of the date of the injury. Instead, the prorated rate set forth in the approved settlement documents shall control and become the rate for that case.