shall include the following information on initial contact with the first enroute
ATS Unit
So how's the poor pilot supposed to work out which unit that is? Who is "enroute" and who is not? I always interpreted it as "the frequency after tower" too.
However there is no harm with differences to ICAO, providing they are obvious and documented for all pilots to see.
Yeeeees. But there is still a workload cost and potential for confusion in any non-standard procedures. Where there is a specific local reason for a non-standard procedure, it can be justified. But "we don't think ICAO got it right here so we're going to gold-plate the rules in our territory in the hope of increasing safety" is a lousy reason, and fails to take into account the knock-on consequences of non-standard procedures outside that territory.