Nothing they can do now. You can't over-turn a decision, what's done is done and Campillo v Shumenov III will happen. But hopefully they review it in enough detail that mistakes like this can be prevented in the future.
just cause the WBA is mexican based and Castillo is from Spain does not mean that the WBA is reviewing this BECAUSE he is from Spain. Even if they didn't review other bad decisions. This line of logic is really far fetched. Its the same kind of reasoning that makes people believe that Pac is on PEDs just cause his team had conflicting statements.
Funeka/Guzman was for the IBF title. Diaz/Paulie was for the NABO (under the WBO) title. The WBA can't do anything there.
What's going to wind up happening is Shumenov will fight Uzelkov, and should he get past that, the WBA will order Campillo-Shumenov III. That'd be the appropriate decision to me.
Best way to go, IMO, only that Campillo should get the winner of that fight, no matter who. Campillo's got a cut in the fight anyway, he will be sidelined for a few months.