There are some that work. Even Gp4 master can be cheated. Just make a copy of the old (unpatched) gp4.exe and rename it to gp4old.exe. Put it in the game folder and point GP4 master at this exe. You can now edit atleast wad files.
A number of other editors work , eg. Team editor. You can change names of team and drivers, performance and import ready made performance files.
Look around, seek and ye shall find.
Larry
AMD 3000+,Epox EP-8RDA,Ram 1536mb 333 DDr, Rad 9800 pro omega 2.4.96, dx9b, Audigy, MOMO FF,winxp