I stole this from The GL1800 Forum...I don't remember being able to get to the locking nuts 7 and 16. I Do remember removing bolt 14 and moving the spindle to another set of teeth on the gear it slips on to.

Yes the Manual Trans model is adjustable.

Here is where the adjustment is made. (Loosen the the locking rod nuts- #7 & 16.)
Rotate rod until the shifter is where you want it.
Lock down the nuts,and button it back up.

I suggest a short test ride.
To see if you set it to your liking,
Before you button it back up

Shifter.jpg