Originally Posted by
fumje
You can write to UA and request original routing credit since the change was involuntary. That said, FRA-MAN-IAH on LH and SQ should credit equivalent qualifying miles as FRA-MAN on LH (UA8866 is operated by LH). There should be no lifetime miles without any UA-operated flights. The only thing to watch for is PQD.
Well, it depends on the class of service. If OP was on a P fare, the new earnings will probably be less; if OP was on an L fare, the new earnings might well be more. But, I agree -- there are no lifetime miles issues here.
OP: When your miles post, compare what you would have earned under FRA-IAH on LH with your actual earnings on FRA-MAN-IAH, and, if the change wasn't advantageous, write for Original Routing Credit.