I honestly wish there was a mod to get rid of the mines altogether, either that or decrease the explosion radius to something less stupid.

After import the extension changes to from .kvs to .dat - I had to manually change it back to kvx, as per lazy dog suggestion

The mine are now visible for me but they keep blinking in and out of reality, so technically a success

Just replaying SW:Redux on GOG Galaxy.

Can confirm it works there aswell and perfectly.
Its a simple open SW.GRP + file swap, it shouldnt be too much of a hassle for anyone.

Will I have to do this every single time I install the game?

This was driving me nuts, thanks.
Although as others have pointed out I had to rename the updated files to .kvx as they were defaulting to .dat for some reason.

Using the SW.GRP in the gameroot didn't worked for me
I had the modify the .GRP in the 'classic' folder instead, even though i'm still playing the redux version. Weird.

I imported the mine but now I don't understand what to do

Slade is a Doom editor, so it doesn't recognize the files.

When i imported the file it renamed it to mine.dat for some reason and didn't work. I had to right click> rename it back to .kvx and then it worked.