After finishing the edit, you need to press another button inside Joplin, to import the changes you made. Doesn’t work automatically.

You can only edit single files like that. If the file contains links to other notes, they are not resolvable.

It is not possible to just create some Md files and let Joplin index them and watch them for updates.

There is a hotfolder plug-in, but it only imports those files and then deletes them.