DerGolgo

I've kept on trying to rule out the culprit and, finally, found it. Maybe.
But when I start the game without Fusebox, everything looks normal once again.
 
DRIVER_IRQL_NOT_LESS_OR_EQUAL is the most common error message, but not nearly the only one. The only filename I've ever gotten was a windows .sys file. I kept googling the different error messages, most suggest a faulty driver, which was why I had first spent days trying different drivers for my Radeon card, installing any existing updates for any number of other drivers, and updating my BIOS. Eventually, I had ended up reinstalling my old nVidia video card and drivers.
The last BSOD came with that IRQL error, after I had put "EasyBoard" and "EasyVesselSwitch" back in, though I'm personally skeptical it was either of these. Presently testing them out.
That last BSOD was also the opportunity for me to switch back to my newer video card, and to install a new driver that seems to have dropped in the last few days (or that I had earlier tried downgrading from and forgot).
I can at least be pretty sure that, if all those BSODs had the same cause, it's not the video card, nor its driver.
 

Start the game in OpenGL mode.
Open the command prompt, go to the game directory, and enter the name of the game's .exe file, followed by a space, followed by -force-glcore
I use the 64bit Windows version, so for me, it looks like this: Ksp_x64 -force-glcore
This will start up the game, and all is happiness and flowers and yipee!

But you ask:
I didn't grow up with an 80286 running MS-DOS 3.1! I don't know how to command prompt! I never even wrote a new autoexec.bat so I could play Space Quest V!
Well, I have nothing better to do this exact minute, so here you go:

Step 1: hit windows-key + r

Step 2: in the little window that comes up, enter the following: cmd
Hit Enter.

Step 3: you should now see the black command prompt, it should say something like C:\users\yourname> with the cursor blinking on the right.
Enter the following: cd.. and hit enter. That is the letter c, letter d, and two periods, those ain't a typo.
Repeat until it says C:\> with the cursor blinking on the right.

Step 4: Now we go to the game directory. Just enter cd, followed by a space, followed by the folder name.
For me, that's cd Kerbal Space Program
Then hit enter.

Step 5: As explained above. For me, with the 64 bit version, I enter Ksp_x64 -force-glcore and hit enter, and puppies and candycakes 'n stuff.
That is, the game starts up in OpenGL mode, and stops crashing, disappearing, freezing the system, or raining down BSODs. Will, instead, behave as it should (in as much as a modded install has any way it "should" behave).

Postscript:
There is probably, no, definitely a simple, easy, elegant way to make a shortcut do it, start the game in OpenGL mode.
I, however, have not found that way, nor any complex, difficult, clumsy way of doing it. So I cannot speak to that.
Doing it with the command prompt as described here, however, works.

I've checked all crossfeed settings. When the flow priorities checked out, that was the first that had come to mind. I have manually inspected every single part. Every crossfeed is on.
Engines are LH2-O, "Sarnus-HE2JT-250K "Tohces-P" Cryogenic Aerospike, inflated with tweakscale. Bipropellant, 93.75% LH2, 6.25% O. Indeed, there are engines that will only draw hydrogen from the tanks. The atomic engines, for instance. Those tend to have a red flame, though.

I've been playing KSP for some time, I am quite sure that any flaws in operation or execution of the design can be ruled out. I believe it either is a fundamentally flawed design, one that just will not work in game. Or it requires special design considerations that would be pretty specific for this sort of problem.
 

Alas, I have gone the way of the big hammer.
In case anyone else encounters the same dilemma, here's how I bested my ill fortunes:

- backup "GameData", "Ships", and "Saves" folders outside the KSP installation folder.
- ensure that any mods you had so eagerly updated for the new 1.3.1 version are downdated to their last 1.3 state.
- uninstall KSP and delete installation folder.
- install KSP 1.2.2, as available on the KSP website.
- immediately patch it to 1.3 with the patch that's also provided on the KSP website.
- copy the backed-up "GameData", "Ships", and "Saves" folders and merge them with the folders in the fresh KSP install.
- start KSP and re-adjust all the little settings that you probably didn't have to loose like I just did.

So that's that. Thank you, @linuxgurugamer, for the assistance!