no you can't
I don't think you can re challenge a gym leader you have already beaten in Pokemon white.
You can't battle them again
sorry but no
you don't you just go up to them and do it again.
Yes, you can take the Royal Unova Challenge again.
You cannot rebattle Gym Leader in Pokemon White.
yes
You cannot re-battle the Gym Leaders in Pokémon Black and White.
Beat them again
In order to "beat" Pokemon White, you must defeat the eight Gym Leaders of the Unova region in order to challenge the Elite Four and defeat them, as well. To do this, you will be given a Pokemon to start your journey with. By catching more Pokemon and fighting other Pokemon with your own to make them grow stronger, you will be able to defeat tougher opponents you come across and eventually beat the game.
Well There is no way to rematch the gym leaders unless if you hack it!
you distract them by letting them pikachu