Manually create mcfx file

I can unpack an mcfx file with 7-Zip of another zip programme. I can then make manual edits to one or more of the four files (meta.json, print.gcode, palette.json, thumbnail.png).

But when I re-compress the file with for example 7-Zip and rename the extension to .mcfx, the palette no longer recognizes it.

How do I ‘re-package’ the four files into a valid mcfx file?

In this case, I want to do this, because I want to make manual edits tot the palette.json file, because Canvas does not ‘send’ the right splicing settings to the mcfx (see topic). But in general, I think it’d be convenient to know how to manually edit the file. I made a second topic, because it is a different question :-)