Are you saying they already crashed into the piston, and you want to stop the VCT from working?
Or that you're afraid they're gonna crash into the piston, and so you wanna turn off the VCT beforehand?
It runs off an electric solenoid, in any case, so disconnecting the solenoid will stop the VCT from engaging. However, that'll probably throw a CEL, and you'll lose top end power, but that's better than putting a valve through a piston. It's part 23796 on the below diagram.
130 Camshaft & Valve Mechanism :: Engine Mechanical :: Genuine Nissan Parts :: Sentra / NX (B13) 1991-1994 :: CourtesyParts.com
No guarantee this won't hurt the engine.