I believe so, but the problem is (if it goes the same way it does on LJ) that once you delete them, they are no longer present in your old posts. So if you have a specific older icon you rarely use anymore and can stand to have as one of your inactives, but is important to keep in your journal because it signals that a older post is from a particular fandom, not safe for work, meta, etc., the icon will be stripped from your journal and the space will be taken over by your current default.