Another way to check is to use your (or create an) Executive Club account on BA, and use their search tool for the flights you want to put on hold. The BA site usually indicates a number of award seats available in each cabin, so if there are a few available, you might be safe to cancel and then place another one on hold. Not sure, though, if BA makes more seats available for Avios redemptions than for partner mileage programs.

You could also use the AA website to just see if the flights you want are still available even with your reservation on hold. You won’t be able to duplicate a booking, but if there is availability, you should be OK to cancel and rebook.

But, if there is currently no more availability, and you need to rely on the seat being released right away back into award inventory, then yes, as others have said, it’s a gamble.