You can install and replace in one go with ${SED} ... > ${STAGEDIR}...

Doesn't Icon=cloudcompare work? If yes, this should be preferred, because advanced DE themes will be able to override the original icon with a themed one.

Not really sure about committing png images into the repo. In textproc/obsidian I just put it into DISTFILES so that the icon gets downloaded during make fetch. I feel like it is a better approach.

I don't think we need a history lesson in pkg-descr.

Please, more on this: how (if) could I do it for both (or many) files in one command? I like the idea just can't get it...
${SED} | cat > ${STAGEDIR} seems to not preserve file names...
Or, I may even not need this as I don't need absolute paths to the binaries at all?

Yes, it does, thanks!

I would possibly follow your advice if I could. As I have to use GH_TUPLE for bundled external libraries and plugins, I can't use MASTER_SITES at the same time. May be, I just don't know how to do it (properly, and at all).

I tried to reword the sentences to your advice.

You'll need a make or a shell loop to do this for multiple files, so feel free to leave it as is if you don't like loops.

MASTER_SITES with a non-default category should work even in presence of USE_GITHUB:

MASTER_SITES= https://../:icon
DISTFILES= cloudcompare.png:icon
EXTRACT_ONLY=

Sorry, but I really can't make it work following your advice: the other DISTFILES - plugins from GH_TUPLE - are failing to unpack properly.
Seems like this port is really different from textproc/obsidian as it has GH_TUPLE which complicates things a lot (at least for me).

Could you, please, allow me to just commit these 2 PNGs to the tree?

I'm not in a position to allow or deny you anything. I just tried to provide some useful input, but if it isn't really applicable to your case - then of course do it your way.

Use ${DESKTOPDIR} instead of ${PREFIX}/share/applications.

Thanks! Done. :)