and perhaps for Move Length and Predefined Commands like Preheat Nozzle?
Not sure what you’re asking here, but all those settings are configurable through Marlin or the slicer.
Which default extrusion amount? On filament change? M603 configures that.
Priming before a print? That’s part of the startup GCODE in your slicer.
Preheat settings? That’s the M145 command in marlin: Set Material Preset | Marlin Firmware
I don’t see those anywhere in a config file. At the extreme end, you could download the source code and recompile with the numbers you want stored in there, but I don’t think that would be worth the trouble.
Yep- been too many years since I’ve compiled code.