This summer when I had a forced overnight in FRA I refused the options LH texted to me that I could stay in. So I booked my own room in the city at a Marriott (less than 130 euros) and LH didn't question paying me. But the forced overnight was a result of LH incompetence.
I do wonder what would have happened if OP who spend 500 euros in VIE wasn't HON. Would LH only pay the 150 euros?
-RM