I've been away from the forum for a short while because I've had a cold and generally feeling tired, disinclined to fight with technology. However, I'm brighter and better now.
Still haven't fixed this issue. I tried svenlind's process from post #31, with a variation.
I create three yaml folders:
one containing virgin, unpatched yamls,
one containing the ones with the original edits
one intended to copy the edits, ensuring I made no errors in spacing etc.
I also didn't unzip the kobo-update-4.30.18838 file (which I did before).
My first attempt was with the original, edited yamls. This failed, but I was given a lot of error stuff I don't understand.
I tried with the virgin, unedited yamls. This also failed.
This is the error gobbledygook:
kobopatch 653070c
https://github.com/geek1011/kobopatch
KoboPatch::LoadConfig
reading config file from *os.File
unmarshaling yaml
| {
| "Version": "4.30.18838",
| "In": "src/kobo-update-4.30.18838.zip",
| "Out": "out/KoboRoot.tgz",
| "Log": "out/log.txt",
| "PatchFormat": "kobopatch",
| "Patches": {
| "src/libadobe.so.yaml": "usr/local/Kobo/libadobe.so",
| "src/libnickel.so.1.0.0.yaml": "usr/local/Kobo/libnickel.so.1.0.0",
| "src/librmsdk.so.1.0.0.yaml": "usr/local/Kobo/librmsdk.so.1.0.0",
| "src/nickel.yaml": "usr/local/Kobo/nickel"
| },
| "Overrides": {
| "src/libadobe.so.yaml": null,
| "src/libnickel.so.1.0.0.yaml": null,
| "src/librmsdk.so.1.0.0.yaml": null,
| "src/nickel.yaml": null
| },
| "Lrelease": "",
| "Translations": null,
| "Files": null
| }
KoboPatch::OutputInit
KoboPatch::ApplyPatches
KoboPatch:

penIn
Opening firmware zip 'src/kobo-update-4.30.18838.zip'
--> open src/kobo-update-4.30.18838.zip: The system cannot find the file specified.
This means nothing to me.

It appeared in the Out folder.
Oh, and I've been unzipping the patch using the Windows Explorer 'extract' feature.