add any "Default Applications" and then "Added Associations" in the first mimeapps.list

make a blacklist with the "Removed Associations" in the first mimeapps.list

add any "Default Applications" and then the "Added Associations" in the second mimeapps.list, except those in the current blacklist

append to the blacklist the "Removed Associations" in the second mimeapps.list

repeat the last two steps for all subsequent mimeapps.list files

finish by adding the mimetypes listed in the .desktop file, except those in the blacklist