Can you make a new class?

[Taurinus]

Yes, you can modify the way skills are handled on the server side. You will need to know C/C++ to get anything done.

[ChaosSlayerZ]

a class cannot be created from the scratch, but can be heavily modded.
Its impossible to give new skills to a class (even if they altered server side, the client still governs who gets what and when), but you can alter their caps per level.

And of course all spells and disciplines are fully customizable.

I have done some heavy modding myself, and basically "created" as many as 6 new classes

No C++ coding was required =P

[Taurinus]

I suppose it depends on how/what you want to mod. For instance, if you wanted a ranger to have the block skill (even though the client cannot allow you to train it) you can factor it into the server code when doing avoidance. So its not impossible, it just requires some c/c++.