I'm giving up, for now at least. I suspect FDev have added an integrity check that finds differences in the compiled shaders (possibly hash-based). It looks like 3Dmigoto compiled my shader okay (says the logs) but it just breaks ED.
What to do:
1. Download the latest build of 3Dmigoto (
3Dmigoto-1.3.12) from
https://github.com/bo3b/3Dmigoto/releases
2. Extract zip into C:\Program Files (x86)\Steam\steamapps\common\Elite Dangerous\Products\elite-dangerous-64
3. Run ED Horizons 64-bit
4. Go to training, combat mission (quickest/simplest way to get into a cockpit with flight-controls)
5. Search for the pixel shader by using the numpad 2 (The shaders turn off as you select them. The "star-dust" will disappear or freeze when you've found 5a0ee5adb1328135.)
6. When you've found the pixel shader, press numpad 3 to save the shader into the ShaderFixes subfolder
7. Open up the 5a0ee5adb1328135-ps_replace.txt file in ShaderFixes in notepad or some other text editor
8. Figure out a way to disable the shader and save the file -
nothing I've done here has worked!
9. Set Hunting=0 in d3dx.ini (it's in the main
elite-dangerous-64 folder, where you extracted the zip file contents) to turn off shader hunting. You'd want to turn-off other options as well, such as logging, once you were totally happy that it's working.
Other instructions are at
https://github.com/bo3b/3Dmigoto/wiki/Using-3Dmigoto-to-find-and-fix-shaders
Good luck to anyone who can take this forward. I might try again but I've taken out a whole evening trying to get this to work and I'm feeling deflated. It took me a week of constant searching to figure this out the first time around, I don't have much enthusiasm to go through it all again.
The biggest problem I have now is that I don't think I can go back to ED without Dustbuster! It seems like such a great update too.