For modded Xbox rosters, overwrite the files (database.big and hist.dat) found in the Database directory with the current files I have included in this release. For precautionary purposes, you may want to back up your current database.big and hist.dat files. Once your game is loaded, what I usually do is go into the Free Agent players list and minimize all players that are CPU-made players (for pitchers, drop them to 1 star Star Power and set their Stamina to 10 and their fastball pitch control to 10). For position players, set their Star Power to 1 star and drop their Hitting/Power ratings to 10. Be sure to save your rosters afterwards (I save mine as 2020 Rosters) so when you restart your game in the future, all you have to do is load your rosters.
For PC users, just copy and overwrite the 19 .dat files found in the Database directory. Again, you may want back up your current .dat files for precautionary measures.