From the launcher you'd be able to click on the mods displayed and install them. The launcher keeps the client-side download percentage updating, downloads the file from the doukutsu club server, then unpacks it into the user's preferred install directory for the given mod (which would probably default to a generic mod install directory)
I hope this isn't considered an unwanted bump (I also got the email), but:
As someone who has casually enjoyed Cave Story mods in the past, a mod launcher, even a buggy minimal one, would be really appreciated.
Edit: before I talk more about that, I thought I ought to mention that
the modding wiki almost certainly qualifies for Indie Wiki Buddy which will automatically redirect any user of the extension away from the old Fandom wiki to the new(er) independent one. There's a form on their home page for the purpose of requesting that a redirect be added.
As for my old mod installation method:
In the past, I managed mods by finding the file, downloading the zip to my downloads folder, extracting the zip while trying to ensure I don't end up with Downloads\doconfig.exe by mucking up folders during extraction. Then mucking about with profile files, if I was upgrading the mod, occasionally losing progress by doing the transfer backwards and overwriting the wrong file (modern windows file explorer makes such tasks so tedious I rush them).
Even though I could have a folder specially for cave story mods, in practice I'd let things pile up in my downloads folder, and then sometimes rely on bookmarks or sifting through search results () to find the zip online again when returning to the playthrough after a break, only to find I already had the files needed.
All this is the sort of thing that nowerdays I'd probably want to try automating somehow, either by using a pre-existing tool built by the community (e.g.
Everest/Olympus Celeste), misusing an existing tool, or mangling HTML with Python (if I was feeling very confident/bored).