Is there a CLI utility that allows one to sync up with their iCloud calendar (i.e., iPhone calendar on the cloud) to modify calendar events, etc.?
According to this release note for version 18.104.22.168 from 26 May 2014, syncevolution offers basic iCloud interoperability:
It now [...] works with iCloud. However, syncing with iCloud ran into a server bug (reported as 17001498 "CalDAV REPORT drops calendar data") and needs further work.