Remember the number of slot that your dynasty is saved on and quit the game. Then go to this directory:
My Documents -> NBA Live 2004 -> saves
Choose the number of slot with your dynasty and open the players.dbf file with DB Commander. Then just find the lines with your players and find the fields responsible for exact ratings. You can put whatever value you like from 0 to 99.
If you don't know which fields are responsible for which ratings, check
this.