How do I install a different shift knob?

The shift knob is just screwed onto the shifter. Grab it tight and turn it counterclockwise. Use lots of force, it will begin to unscrew. Just screw the new one on, or mount it in place with lock bolts if that is required.

Many 1990-1992 owners find the 1993-1994 shift knob a nice replacement.

Thread pitch on 1G/2G shifter is M10 x 1.25mm
This thread pitch is shared with some mazdas Ex: Mazda 3 Miata MX3 MX5 MX6 Eunos Protégé 5 323 626 Mazdaspeed JDM