You can edit any player and their abilities, and not just the way they look. 
Sign a desired minor leaguer to the maximum term (seven years) at the lowest 
amount, even though they may get upset later in their career. Then, change their 
name, abilities, position, etc. This also works for changing other major league 
players. For example, you can change Joe Young on the Giants to Barry Bonds by 
editing everything except his appearance. By doing this, you can sign an entire 
team. Note: You can only re-negotiate contracts at one year to seven year 
contracts at about $1 million each or less, then make them perfect. When you are 
finding a player to make your own, look for one year contracts.