Sonotsugipaa

For the first question’s answer, that doesn’t work if the directory’s file system supports extended file attributes, as Dolphin will prioritize those above the .directory file.

If I had a penny for every time I found out through the fediverse that my current anime pirate streaming website of choice shuts down, I’d have two pennies.

Which is not a lot, but GOD FUCKING DAMNIT

A quick search tells me you need to open the directory’s properties dialog and click on the icon on the top left; if you want to set directory icons programmatically maybe you can do that, then try and see what Nemo does in order to change it?

Otherwise I’m afraid you’ll need to seek some documentation for Nemo or GNOME Files (since the former is a fork of the latter), or at worst, Nemo’s code itself.

Not sure how it works on other file managers (or any DE), but for Dolphin you can create a .directory file with its content like:

[Desktop Entry]
Icon=/absolute/path/to/image.png

I think it’s more or less universal.

Specifically for Dolphin, there may be a way to achieve the same with extended file attributes (getfattr/setfattr) instead of directories, but I don’t know the attr name for icons if it even exists.

Fortunately the USA wouldn’t act against foreign entities on the whim of a few companies