I think a 134 retrofit kit is like $8 at Autozone. It comes with the high and low side fittings and the longer schrader valve tool (~ half inch instead of the quarter inch long?).

I can't see the need for a whole new hose unless the threads on one or more of the parts are stripped: 134 valve onto the R-12 port, new schrader into the 134 valve.

If the 134 conversion were done 'correctly' and the old fitting is trashed, then you might need a new hose. There's supposed to be loctite on the 134 fitting, but mine just unscrewed with a wrench.