You're looking for a mod feature for Fight Night Round 3 on PSP. Here are a few possibilities:
Often hosts older community "modded ISOs" that have been pre-patched with custom music or rosters. 4. Technical Hurdles If you are looking to mod the game yourself, be aware that: ISO Rebuilding: You'll need tools like fight+night+round+3+psp+mod
Fists of Glitch: Round 3 Reloaded Platform: PlayStation Portable (PSP) - Custom Firmware Mod Type: Gameplay Overhaul & Graphics Injection You're looking for a mod feature for Fight