Follow these steps:
1) Create a backup for your NBA 2K14 folder where Kevin's roster files are installed.
2) Reinstall NBA 2K14 so you get to have the original files of the game.
3) Delete the Online Data folder.
4) Open your newly installed NBA 2K14 (original files/the one without any mods)
5) Load up your My Career that you would like to mod as Russell. (100% sure that your player would be headless or glitched but it's okay).
6) Open the trainer then select Russell then change everything you want like your minutes etc.
7) Save it then close the game.
8) Open your modded NBA 2K14 (Kevin's mod) and enjoy playing My Career as D'Angelo Russell

I hope this helps bro. About 2 years ago I used to have this problem but I was lucky enough to find a solution for this.
Enjoy