RED Modding Center (aka RED MC) is the definitive editing tool for NBA 2K13 and NBA 2K14. Use it to externally modify roster files (PC, PlayStation 3, Xbox 360), import to and export from .iff files (NBA 2K12-2K14 PC), and edit MLB 2K12 files (PC).
Instructions on how to purchase licenses for all the tabs can be found here.