I read somewhere that this is strictly against policy because by that they "unmarry" a married segment. If a call center worker does this these days, he or she would be severely punished. Even on a new booking, he or she is no longer allowed to add segment by segment -- the whole itinerary (one way) has to be entered at a time to avoid the chance of un-marrying a married segment.
HTB.
Maybe a no-go for LH agents but every experienced TA would do it exactly like that. And if Amadeus makes an autoprocing for the Itin then, so what?