How do you add dynamic wallpapers on immutable KDE?

There are 3 (!) apps on Flathub for adding custom Dynamic Wallpapers to Gnome:

Especially the last one is pretty great, as it allows time-based light/dark with different levels in between. But focusing on the one in the middle, it simply creates a Gnome-compatible Wallpaper pair with all the tags and everything.

Its simply a folder in ~/.local/share/backgrounds/ with a name, containing an image name-d.FILE and name-l.FILE thats it.

Its pretty great but KDE uses a different syntax, what I found in /usr/share/wallpapers:

Name-of-Wallpaper/
   metadata.json
   contents/
      screenshot.png
      images/
         exact-size-vertical.png
         exact-size-horizontal.png

yeah, thats a bit more complicated, but now my question is, on an immutable System, how do I add more of these pairs?

I tried replicating this to ~/.local/share/wallpapers and they appear (without a screenshot but works anyways), but they dont seem to switch day/night when I change the theme?

Also another question, how do I just change the color scheme, and not the whole plasma theme? I found no CLI argument to do this, and addons like “color scheme swapper” dont work at all anymore (using breeze dark and light) or they also change other parts and not only the colors