There was something in FSUIPC for FS9 (I have the registered payware version) that has something to do with the increments in panels.
"A set of “fast†FS autopilot value increment/decrement controls. These add to the default FS “inc†and “dec†controls
with ten times the increment. Values handled are Altitude, Speed, Mach, V/S, Heading, and both OBIs (Courses)."
This is the opposite of what you are looking for but but this section is titled Fix Control Acceleration.
Again, this is a paid registration version of FSUIPC4.
The is also some button functioning for inc and dec granularity in the advanced user guide. If you install with paid registration active you'll get the standard and advanced user guides in the FSUIPC FS9 folder (in .pdf format).
Now Ken programmed his panels from scratch so maybe he had something in there.