Apart from a command upgrade program - ICUS is merely a backdoor invented by ICAO to allow CPL holders to get to ATPL level without having enough command hours. The meaning was extended because of cadetship programs, as an average cadet will not have more than 100-120 hours of real command time at the end of the program. For a former cadet, ICUS time is only relevant until ATPL PIC time requirement is covered.
There are no restrictions for logging ICUS after getting up to ATPL reqs - it becomes a simple designator between PF/PNF legs up until FO gets promoted and starts a real command training. Only at this point in time ICUS becomes what it is supposed to be: command under supervision.
PS: I still don't get how is it relevant to the thread subject
