The valve 'fails' open. I think the valve is closed at idle and low rpms, after that is when it opens. So when disconnecting the cables, it stays open all the time.
It defiantly louder at idle as I've can hear side by side with dads bike that has not had the mod done.
Even though people will argue if it affects performance at low rpm. I cannot notice any difference at all. I really think its there to dampen noise it idle.
As for removing the cables. You should not have any problems at the valve end as you can see everything (remove the exhaust heat shield). At the other end is a bit more tricky as its very confined, hard to see, cant get fingers in, etc. Some people remove the tank to get access more easy, but me and others did it by pushing on the cables to line up the cable with the exit slot of the servo and used a screw driver to dislodge the cable. In the end it was very easy, but its fidgety. Keep your cool, haha.
Have a read here too. More information.
http://www.mvagusta.net/forum/showthread.php?t=45994