When I got a look at the key fob from the parts car, I found that it was empty and did not have the remote locking electronics inside, so I couldn't test it.
As Markus noted, the M531 and M535 modules differ in that the standard M531 box does not have the remote locking function.
Looking at the factory service manual, and my various cars, it seems that the wiring harness to the module changed in 2001. The 2000 and earlier cars have the remote locking antenna wired into the main connector. The antenna on the 2001 and later cars is a separate connection.
If your connector has a heavy wire to pin one and a ground shielding wire to pin 22 (they join together in a black sheath), then I expect that your harness can support an M535 module from 2000 or earlier. (Note my signature for disclaimer)