my friend uses pokegen to get good stats and pokemon and wanted to put black Kyurem
in pokemon black so i wonder will it mess up his game
I am not sure if it is even possible to trade Black/White Kyurem from BW2 to BW1, the game may prevent it. However, if it is possible then it will just become regular Kyurem as there are no alternate forms in BW1.
It shoudnt do anything becasue you just trasfering a pokemon you all ready have/in the pokedex in a differnt form.Its kinda liek trade a shiny between games.