Connection of the play-by-play names to different players is done in the NFL2K5 roster editors. Changing the Photos can also be done in the editors. Adding photos is not done. The Photos are stored on the game disc, not the gamesave file.
The only way that I can think of to make this possible would be to:
1. With the PS2 version on PC (using PCSX2), use resource substitution.
2. Figure out how to hack the game to do resource substitution.
3. Get the source code from 2K, figure out how to modify & re-compile the game.
#2 is unlikely (~80 unlikely) to happen.
#3 is very unlikely (~99.99% unlikely) to happen.
#1 would be the easiest to do.
Perhaps using Texmod (google "pcsx2 texmod")