I am not sure they will be able to over throne Real Madrid who we are very sure will continue to perform excellently in the next football season.
LaLiga will start 13/8 in two weeks we will wait for the season to start, about Barcelona beating Real Madrid there is a possibility although I think it is still quite big but I believe Xavi is a good manager with all his strategies and can bring some players are suitable for him.
Bringing in a lot of good players doesn't mean that the team will play well. Barcelona have to prove themselves first in the liga, it was just a friendly match and to be honest I'm not sure if they could win the Classico in the league. The players are new to the team and will probably need a season to settle in properly.