Change macOS Mojave login background? (boot / screen saver)

Finally upgraded to macOS Mojave this week.

Noticed two annoyances that will bother me (multiple times) every day:

  • The login screen, at boot, shows the Mojave desert picture, instead of my solid color background
  • The login screen, after the screen saver was active, shows an overlay over the screen saver, instead of my solid color background

Any way to fix this?

Note: I have FileVault turned on and rather not turn it off and on again, as the decryption/encryption took more than a day last time I did that…

So I’m looking for something better than this (if possible):

I found a workaround for that: add and remove a user using fdesetup instead of disabling/enabling FileVault.

Using the hack in the link (replacing the Mojave.heic picture) I was able to get a solid background for the login screen at boot time.