Executable is the problem.
And if you bought original game (version2) it's not crime to switch executable (if you can find it).
Crime is to download it from net.
Ah... Crime...
Z Modeler 2,of course,but you have to pay to be able to import.
3ds Max can do it too but it's expensive.
And editing CJ is VERY VERY hard job.
He isn't made like other characters.
GTAForums is place for info.
It's done through editing main.scm.
You'll need san andreas mision builder to edit main.scm.
There are couple tutorials (by yeti) at gtaforums.
They are quite simple,everyone could do it.
But gtaforums site is down at moment (or permanent).
Only bad thing is that your old saves won't work.
There is a way to fix it but it's hard.