If the cable was never to be adjusted, there probably would not be an adjustment screw installed on the cable mechanisn in the first place.

My W123 service manual contains no prohibition on cable adjustment, although it does indicate that the shoes should be the primary means of parking brake adjustment. Cable adjustment is indicated when the cable or axle has been replaced. Obviously, the cable needs to be adjusted if it has been removed in conjunction with some other job, like removing the driveshaft.