Modifying an existing desktop file's MimeTypes

[Jerome Leclanche]

Consider the following use case:

"gimp" supports image/png. "gimp-webp-plugin" makes gimp support image/webp.

How would gimp-webp-plugin declare that it makes another app support
additional mime types? I don't think it's possible currently.
Suggestions?

Mime actions could theoretically do that (in a system-level
mimeapps.list), but most package managers do not have the ability to
modify a file shared by multiple packages (we'd have to create
something silly like /usr/share/applications/actions.d/).

J. Leclanche