Since submitting a ticket did not resolve this issue, I am reaching out to the swarm for possible clues on this one:
So I have downloaded the newest installers for the 77L and 77WL, uninstalled, reinstalled (as was advertised by the devs in preparation for micro-updates) and now suffer major problems with the OC and the 777 product.
1) The OC can not repair the liveries for the 77L I had installed because it is unable to "load the back-up file".
2) The 77W is missing from the OC and the sim entirely, despite installing properly and without error messages.
3) The install somehow messes up my Visual Studio C++ runtimes, as PFPX starts to randomly crash and bug out (like not being able to add aircraft into the database). This is usually resolved by uninstalling and reinstalling the Visual Studio 2015 C++ runtimes, both x86 and x64.
It still does not fix my grievances with the 777 though, as I am unable to use either variant as before. I could delete everything PMDG-related from the sim folders, but am reluctant because of the accumulated hours on different airframes and not wanting to mess up things further.
In addition to my hardware specs, I am running Windows 10 Pro x64, my sim is not on the system partition and I always run everything FSX related on the Administrator account.
At this point I would love to downgrade my OC and revert to the old installers, as these worked without a hitch.