I decided to take a chance and reach out to SpeedDemon95. After a few messages back and forth, we arranged to meet at an abandoned warehouse on the outskirts of Milestone Springs. The meeting was set for midnight, and I was instructed to come alone.
NFS Payback features an "AllDrive" system for multiplayer. Using a modified save file generally works for roaming, but there is a risk of being flagged by anti-cheat systems if you participate in specific online events. However, since the game's servers are peer-to-peer and the active player base is smaller, bans for using save files are rare but technically possible according to EA's Terms of Service. nfs payback 100 save game all cars
That being said, here are some general details about Need for Speed: Payback save games: I decided to take a chance and reach out to SpeedDemon95