I have over the years only changed a BAH a couple of times, IIRC one was a about £150 more and one was about £18 less. As others have noted, some you win and some you lose. IMHO if you have to change due to external events, just do it.
Far better to sometimes absorb a little extra cost than miss out on something else. Ten years from now, you will have forgotten how much you saved (or had to pay extra) but you won't have fogotten how much you enjoyed the wedding!