This default.lua file when placed in the location specified by the file structure within the zipped archive will add the extra bindings:
3 Position
"Alternate Flaps Up"/"Alternate Flaps Down,"
"Alternate Gears Up"/"Alternate Gears Down"
"Alternate Landing Lights Land"/"Alternate Landing Lights Off"
"Alternate Weapon AA Mode - IR Missile"/"Alternate Weapon AA Mode - SAR Missile"
"Alternate Radar On"/"Alternate Radar Off"
"Alternate RSBN Mode: Descend"/"Alternate RSBN Mode: Landing"
"Alternate Nav Lights Min/Off"/"Alternate Nav Lights Max/Off"/"Alternate Nav Lights Max/Med"
"Alternate Low Altitude Antenna Tilt"/"Alternate Low Altitude Filter Off"
2 Position
"Alternate Gears Handle Lock released"
"Alternate Airbrakes On"
"Alternate Emergency Afterburner On"
"Alternate Engine Emergency Air Start On"
"Alternate Nosegear Brake On"
"Alternate APU On"
"Alternate Master Mode - Air"
"Alternate Landing Lights Land 2 Position Only"
"Alternate Weapon AA Mode - IR Missile 2 Position Only"
"Alternate Afterburner/Maximum On"
On the bindings with 2 options simply bind the up and down/on and off position to the respective positions on any of your 3 position switches, for the single bindings simply bind it to any of your two position switches. In this way the 3 position switches will have their middle position function as you would expect and the 2 position switches will have their down position function as expected as well.
This thread http://forums.eagle.ru/showthread.php?p=2289411 explains in detail the format of the keybinding lines in the Lua.
If anyone has any requests for other modified mappings I can look into adding them to this file.
10/05/2015:Sorry about not being around for a while, got busy with a house move and some things, I have ported my modification for the MiG-21Bis over to the DCS Beta now and have confirmed the functionality of all of the bindings except for "Alternate Landing Lights Land"/"Alternate Landing Lights Off", "Alternate Landing Lights Land 2 Position Only", and "Alternate Nav Lights Min/Off"/"Alternate Nav Lights Max/Off"/"Alternate Nav Lights Max/Med". The light related binding have been disabled until I have the chance to dig into the changes made regarding them to get them working again, also "Alternate Afterburner/Maximum On" appears to be buggy right now, the switch makes the moving sound when the corresponding warthog switch is flipped either direction and according to where the green cursor for flipping it is the switch is in the correct position however visually the switch appears stuck in the down position, I have not had a chance to test however the switch binding may function adequately. If anyone can chime in about whether the "Alternate Afterburner/Maximum On" binding is working or not that would be great, otherwise it may be a day or two before I have the chance to test it more. MiG-21BIS Custom Controls.rar MiG-21BIS Custom Controls (Beta DCS).rar