Re: Low throttle setting as "kill switch" when stopped...
The weak link in the button style of locking clutch levers is the small 'C' clip that holds the button in the lever. They will snap off allowing the button and spring to pop out. I drill the button shank where the 'C' clip groove is and install a 1/16" cotter pin. I also put a 3/32 I.D rubber 'O' ring under the cotter pin. That reduces the shock to the pin when you release the lever and also stops that annoying "click" sound.
As for clutch cable slack. I don't allow any. I don't make the cable bowstring tight but there's no slack in the cable at the clutch actuating arm when the lever is released. My clutches are fully disengaged when the lever is locked and there's no slippage when they're released.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"