I don't think you are on a sure footing here. BAC have said that they would apply the conversion for flights booked before 30/12 but what happens to flights changed after that date is a bit of a grey area.

I understand that your opinion is that you should get the best of both world (ie the booking as involuntarily changed and presumably more generous TP wise as a result of the cancellations, but still with the pre-30/12 conversion) and I personally don't find your interpretation unreasonable, but equally, I certainly don't see it as the only reasonable interpretation there could be, and BAC's own (that in effect, if you want the conversion for the old booking, it should be on the booking as made initially, ie through ORC), whilst unfortunate, is not unreasonable either.

So to me, you are not the victim of an "incorrect" adjustment here, just of an adjustment that you had not seen coming and which is not the one you were hoping for. So personally, I think I'd probably accept it as such.