The lug bolts hold the rotors on in the W124 chassis, front and rear. No need to replace.
Basic rule on bolts is to re-use unless they are subject to stress or head that would change the material characteristics.
That means stretch bolts (these are always tightened to a torque and then some degree of rotation) and critical fastners like the bolts on calipers should be replaced unless integrity can be verified. Mind you, I've never replaced a caliper bolt and never had one break, but if the factory manual says replace, it's a good idea. Some manufactures (Volvo, on the TD) require replacement for head bolts each use, others have a length spec.
The newer cars have many bolts "glued" in with Loctite, and it's a good idea to either replace the bolt with a new one coated with the microencapsulated adhesive OR to clean it off and use the appropriate color of loctite. On large bolts, you also need to clean the threads with a thread chaser in the body so that you can correctly torque the bolt.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!