I would stay away from BA the fees are a killer and instead Id use the BA miles for non-stop short haul AA flights in the US eg NY-Miami is 15k AA wanst 25k

what you will need to do is call a carrier from each alliance and ask what if anything they have for 8/4, but you will need to be flex in 2 ways 1- the day of your return and 2nd the cabin = if you will only settle for Business class and on 8/4 its most likely you will end in failure

Then if you dont have top status in that Alliance you will be stuck with what they have (except CO allows changes for $0 up to 21 days out, not sure if its from the original date of the outbound or just the Inbound)

CO shows nothing at all on 8/4 , on 8/5 its PRG-BRU and 8/6 BRU-EWR both in Biz although the IntraEurope flight is really a coach seat

on 8/5 or 8/3 in Coach you can fly PRG-FRA-JFK and the FRA-JFK is on SQ(Singapore on the A-380)

last summer I changed my flights at least a dz times as better routings and days and times became avaialble, but the routing and times I really wanted never was avaialble. But with top status I always had the option to redeposit the miles w/o any fees, w/o that top status you may find yourself not being able to fly on 8/4 and in Biz