Sorry for taking so long to respond here. I can't answer all the questions, but I'll have a go at some.
1 - Who designed, created and 3D modeled the F-69 VTOL ?
Justin Miller, who's since switched from Vehicle to Character art. He modeled it, loosely based on a concept from a company called WingKing, but he made a lot of improvements to the design.
2 - Is it possible to edit the decals and textures or is the SDK required to do so ?
It should be possible to swap out the existing decal textures with new ones - I'm not sure if the SDK is needed to do that, or if there are third party tools that will let you open and save them (I think it's a fairly standard file format, so there should be external tools, though we might be using the standard in a non standard way). It may also be possible to add a new set of decals, and a variant, but I think that would need the SDK, and be a lot more complex. I also don't know what the decals are called off hand - I would expect they would have some identifier as being a VTOL or STAG decal though (like VTOL-Dcl or Dcl-Stag, or STAG-DF, something like that. DF would stand for Distance Field, the type of decal used - Now I think of it, Distance Field textures might not be possible without the right tool, so that might need the SDK)
3/4 - Since the Saints F-69 VTOL already has decals, would it be possible to edit them as shown below? Is it possible to edit the textures of the F-69 VTOL to get these results shown below ?
Sort of The problem with painting the VTOL is adding decals where none exist on the original, and that some of those decals are based on the underlying polygons, so their shapes may be stranger than you'd think. One example of a potential issue with your examples is that one has lightning bolts at the front under the cockpit. Since there is no decal there on the original I doubt it's possible to add those.
8 - Does the F-69 VTOL spawn like this purposely or is it a spawning script glitch or oversight ?
That's definitely a glitch
9- Since the above spawning anomaly occurs, is it possible to edit the F-69 VTOL code via it's animation states or spawning states script files ( not sure which files they are ) in order to make it be in the state shown below ? ( Landing gears down, all wings straight, rear intake doors closed and canopy down )
There is probably a script or file that references which animations play and when - You could modify that to lock it into one place, but that's outside my area of expertise, so I wouldn't know where to begin.