IIRC, date/time (but not routing) changes are free of change before and after departure on Star RTW tickets. I wonder if the problem was that you were trying to make a sand day change (as in, essentially standby for a later flight). That may have been treated differently (or in fact, the issuing agent (LH?) perhaps didn't know).

Or, the rules could have been changed, but I had always understood date/time changes of flights was FOC.