If your game crashes after installing a new outfit or face mod: Delete the corrupted playerped.rpf in your cdimages folder. Find your backup (e.g., playerped.rpf.bak ). Rename it back to playerped.rpf . Restart the game to verify Niko loads correctly.
For those serious about long-term modding, community experts like those found on GTA modding blogs suggest creating "portable" installations of the game so you can have one version for heavy modding and one vanilla backup version for clean play. gta 4 playerpedrpf backup