The latest client is not much different to the previous one, apart from they have encrypted nagravision dll's.
The problem with the newer version, is not the exe itself, but something to do with the kernel / filesystem as we cant seem to execute files outside of the windows folder again...
The best way we found to mod the code was to use ILDASM, and ILASM.
If modify a copy of the exe, and change all the private methods to public, you can then create a new project in visual studio and set a reference to your modified exe.
If you want to modify a class or method you can then use reflector, and paste the class into the project and use all the types and methods from the original exe in C#
Compile your project... ILDASM it, and then paste the IL code from your modified methods back into the original ILDASM, and recompile.
Mick