They are called the ability's raw codes, and usually begin with an 'A', and are capitalized, as they are integers (hexadecimal numbers).
But to anwser your question, no, there isn't such a function... Units can only be ordered to cast a spell with the ability's command string (like "thunderclap", "thunderbolt", "cripple", etc...)
call IssueImmediateOrder()
call IssueTargetOrder()
call IssuePointOrder()