Have an option in the admin CP to disable the member list, calendar etc.

You can do it yourself easily by modifying the php but after every update you have to do it again.

Would be convenient.

You can disable member's ability to access these sections in the ACP (don't give anyone access to the calendar under Management tab, disallow members to view the memberlist from the group settings, etc. Then you can remove the links from the skin. You shouldn't have to edit the php files.