The file manager PCManFM has an option (enabled by default) to ask what to do with inserted/mounted volumes (cd, dvds, iso files etc) which is lacking in elementry OS' file manager. That's why I m using PCManFM for this purpose.
When connecting an external HDD:
When inserting a DVD or mounting an iso-dvd:
When inserting a CD:
But can that list be edited somehow in order to add or remove items?
Update after answer:
/.local/share/applications/mimeapps.list contains this:
[Default Applications] x-scheme-handler/apt=apturl.desktop xdg-mime default org.pantheon.appcenter.desktop x-scheme-handler/apt
[Added Associations] , nor
Possibly an elementary-os-specific issue?