I just managed to read your four-fold switch experiment. I thought you were overmaking it, you should achieve the same result with just three switches...
I can tell about a triple-switch that works like a charm, may be it helps, we can use custom move types to help with some "experimental" unit switching:
I configured an Ar-234 which can be configured with recon cameras or bombs, but just in the air base, not while in flight...
Switch 1: Bomber mission payload: Regular bomber stats, regular air type movement
Switch 2: Landed aircraft on base: Fuel same as above, movement = 0, any other stats value = 0, Unit class = 6 (structure).
Movement Type: I created a new move type which allows said unit only to move on airfield hexes. So, if the aircraft is flying (i.e. not on an airfield hex) it cannot switch because the switch button is greyed out.
Switch 3: Recon mission payload: Better spotting, no attack values, just passive air defense (The Ar-234 had two rearward firing 20 mm cannon).
This way, when you are on an airfield, you can cycle without problem to all of the three switches, but after leaving the airfield, the switch button cannot be activated. This was developed from an idea from forum member Intenso82, who is making a terrific modding work.
Too bad organic transport units cannot be made switchable, because as I planned to make a transport unit for a towed gun, we would have avoided the feared "one fuel tank for all" effect...
So, I think a triple switch unit is mandatory: 1) Heavy siege howitzer (I'm thinking about capturable 30,5 cm Skoda M1916 siege howitzers) --> 2) Land transport (Faun ZRS on pneumatic tyres) --> Rail transport (Faun ZRS on steel railway wheels). I am working on some modifications on a scenario made by Nikivdd on the non-historical "Fall Grun", the invasion of Czechoslovaquia in 1938, to include in a custom half historical - half "what if" campaign I am currently (and slowly) working on
