Gatevalve/ turn off tap?

22mm fitted circa 1978 leaking at small nut end ( gland nut) can just centre of gatevalve (tap bit) be replacced leaving main body in place.
No play in pipe work and dont want to disconnect from cold storage tank in loft to replace complete valve.
Obviously drain down loft tank then reduce level of water in hot water tank it feeds to clear pipe of water.
Thanks in anticipation.

Bob UK
July 2016