What is the purpose of this valve, Can i re-pipe the exhaust to a different position. Do i have to use the valve

EXUP type valve? You'll be wanting to keep it I'd guess or you'll be losing a lump of torque somewhere in the rev range.

Exhaust valve on 954 is all about smoothing power through the entire rev range - important for the bikes but not so for the cars, unlike later blades where the ecu needs to see the motor position or you lose a lot of grunt, it is not as sophisticated on the 929/954 - you wont need the valve in the pipework or the motor it it will not lose power
Hope that helps
Andy

Honda HTEV/H-VIX and Yamaha EXUP systems change the exhaust manifold configuration from 4-2-1 to 4-1. This gives the mid range torque benefits of a 4-2-1 and the peak power benefits of a 4-1.

[Edited on 10/2/17 by MikeRJ]