If you mean the straight bar that connects foot control to the gear box (and by unscrewing you mean the position of the foot control moves because the length changes), you need to tighten the nut on the threaded eye-bolt that sets the length of the straight bar. This will secure the length.
Probably obvious, but make sure that the length is set where you want it before tightening it up. The position of the shifter changes quite a bit with length.
This is also a good time to consider whether you are happy with your choice of vertical hole that the straight bar attaches to. The varying positions control how far the shifter needs to be moved to effectuate the shift.
BTW, Sato itself is exceedingly responsive to emails if you ever require their help.
i put n attack folding shifter on my 1198 and the bolt keep svibrating out. Can't really loctite a bolt that needs freeplay for shifter to pivot on.
Also looking at gp shift for the track. Anyone?