Original xbox Checksum Fix for NFS

Im curious if there is a way too fix the checksum on NFSMW & Carbon after modifying the save with a hex editor?
NFS for the Original Xbox seems to be structured identical to PC versions so getting all the bonus cars into your career mode car lot would not be hard provided there is a way to fix the checksum so the save actually loads. Iv tried all save editors and none work but my guess is that's because its coming up with a PC checksum due to them being PC save editors. Any help would be massively appreciated?