OP here with update - I was not able to check the bag all the way through in Arlanda. The agent tried a lot, read the rules, confirmed that the rules have changed now for him to be able to check the bag all the way through to Dallas, so that I don't have to retrieve in London, also spoke with his supervisor, but the system did not allow him to do it.

Finally he just checked it to London. I retrieved my bag in London and went to the hotel. Next day 2 hrs before the flight I checked it in. I could have tried at London to check the bag in again, but did not want to waste my time if they said no, and anyways I had a hotel for the night, and it was just one bag and the hotel was next to the airport so let it go.

Thanks everyone for sharing your experiences.