The operating carrier changes, the OP's changed from LH to EW. It's just further proof there are material changes, because these are two different AOC. The Regulation mandates pax are informed when the operating air carrier changes. LHG have several AOC.

Its just basic contract law isn't it? Something changed. The operating carrier changed, and a lot of things can change with that, even if it's still an EU carrier. It's not acceptable to most people if you book Lufthansa and end up on another company's aircraft, indeed an aircraft registered in another (EU) country. Just as many EW pax experience this past summer with wet leases operated by a Lithuanian outfit.

If LH wetleased FR/W6/B0, would you find that acceptable? They're LCC's as well, like EW. Would you think there is no grounds to complain and ask for rebooking, or refund? In Germany I reckon pax would sue cos the legroom isn't the same as defined on LH.com or they didn't get the bottle of water...or some such. They seem very litigious there.

It's peculiar the EU would have a Regulation that mandates pax are informed when their operating carrier changes if that's not a significant change. Why make carriers inform pax at all, especially in the case of EU carriers? ALL wet leases always say, Operated by xxx for xxx. Moreover, EC261 claims are always against the operating carrier which changed from LH to EW.

I already stated that BA permit pax to rebook when the operating carrier changes. Come to think of it, a few years ago I was able to make use of an invol when LO were using B0 aircraft. Therefore, as I said before, in my opinion the OP can request FOC reaccom on a LH operated flight, as they originally booked. I would say a refund isn't even out of the question, something for the Courts to look at if refused and what the airlines are probably reluctant to allow hearing on.