Hi i'm new here.. but i think it is possible! I used Leftos' roster editor, opened my mycareer file e.g.(yourcareer.cmg), find your player on the Players tab then change the ShoeBrand cell from nike to adidas then change the ShoeModel (go to http://forums.nba-live.com/viewtopic.php?f=150&t=88112&hilit=shoes
for the List of Shoes in NBA 2K13), click the Save Players button then you're done!
hope this help