The reverse switch isn't on the mower deck. You'll need to look at the underside of the tractor. Work the reverse pedal with your hand. Look for where a paddle on the reverse pedal linkage presses against a spring loaded button switch. Bend or remove the paddle such that it no longer contacts the button.
Tractors of the past:
2010 Cub Cadet Z-Force 44 fab
2005 Cub Cadet 2544
1979 Case 220
2003 Yard Machines 17hp 42" transmatic (crap-matic)