Unverified. Before you follow the glitch you must choose to do one of the two glitch(es):

(A) Giving a normal guitarist 'The Scythe'. Go to whatever difficulty you would like to play on, choose the Grim Ripper as a guitarist. Go to select guitar and pick the scythe, (seeing as it was the old one, read (B) for more info). Now select the prefered guitarist, and now he is using 'The Scythe'. He only has the scythe because it didn't go to guitar select mode like in co-operative after selecting guitarist.

-- or --

(B) The Grim Ripper with a normal guitar. Go to whatever difficulty you would like to play on, choose any guitarist (except Grim Ripper), then choose your prefered guitar. Now select the Grim Ripper, it should still have your prefered guitar because it didn't go to the guitar select screen and auto-choose scythe like in co-operative mode.

These two glitches only works in career mode.

Submitted by Berkut (ehs90744)
Correction by memnoc (tjjking)