3 week ago I did a similar trip. We were Abz-LHR-BNA outward & AUS-LHR-ABZ return. Before travelling we realised that my pal may need to finish his journey at LHR since it was likely he would be travelling straight to Germany. So I called the GGL no & was advised this could be arranged at checkin at Austin. He should just advise the agent in Austin he no longer wants to go to Aberdeen but instead will terminate his journey in LHR. So his bags need to come off there.
Please note, however when he requested this at Aus checkin the agent said it wasn’t possible to do this. We explained it was crucial that he got his hold bags off at LHR. The Aus checkin agent checked with his boss & reiterated that it wasn’t possible for my pal to pick his bags up at LHR & they would have to be tagged to ABZ. However he added he just needs to ask for his bags in LHR. Adding this happens every day. We had 2.5 hours between landing in LHR & the next flight to ABZ.
What happened is that my pal initially went to a lost luggage airside in LHR. They said that they thought it wouldn’t be possible in the timescale & that he needed to go out past security & speak to BA. He did this & it all worked out. BA got his cases within 20mins & he terminated his journey at LHR.
After experiencing this my thoughts are. If you can call BA before change the final destination to LHR. The checkin person at AUS should be able to tag a bag just to LHR however it’s depends on the day who you get.
best wishes arranging this