I don't quite understand. According to my information, AppData aside, there must be a
.desktop file (for the application) and an .xml file for the mime type.
%{_datadir}/applications/myapp.desktop
%{_datadir}/mime/packages/myapp.xml
The icons
%{_datadir}pixmaps/myapp.png
%{_datadir}/icons/hicolor/256x256/mimetypes/x-myapp-doc.png
The tool desktop-file-install installs the .desktop file into the appropriate location,
but there is nothing documented for the mimetype and icons.