You will not be able to trade a Resolution Form Keldeo to Black and White. If you wish to trade Keldeo to one of these games, you must revert it to its Usual Form by forgetting Secret Sword.
-http://www.pocketmonsters.net/articles/1359/
As the website stated, you can't trade a Resolution Form Keldeo to Black and White without making it forget Secret Sword, as that is what made it change form in the first place. If you try to make it learn Secret Sword in Black and White, it will not make it transform, as stated here:
To make Keldeo learn Secret Sword in Black and White, put Cobalon, Terrakion and Virizion on your team and head to the Moor of Sekka! However, this will not make Keldeo change to its Resolution Form.
-The same website
Hope I helped! ~atode!~ ('later!' In Japanese.)
