If the shape of the bar is the same (both should be straight across), you may need to stretch the clamp or something due to the larger bar diameter, but as Neil said otherwise you should be able to adjust it with the turnbuckle per the factory procedure.

http://mb.braingears.com/124_DISC2/Program/Chassis/40-0310.pdf


BTW, the 20mm rear sway bar is made by H&R as a W210 fitment, part number H&R HR-71724. It will not fit W124 models with a V8 due to the different (larger) subframe but it should fit all sedans and wagons, and probably the coupe & cabrio as well.