ROM Hack Hacking 3D Classics games?

[RosalinaFan573]

They seem to have *.dat format files on the root of the romfs... How do I modify those files?

 

[Thelostrune]

Use a hex editor and see what the headers say. They should indicate what kind of file is within the archives.
There are .dat extractors, though, so you might wanna start with that.