Dark shader should work in X10 a mate of mine got going in a X10 game he made at least he said he did. In FPSC X10 the majority of the shader files are not keep in the file system they are hard coded into the source code in DBP this is to stop people ripping of things from Dark Shader or where they where made originally made. They do the exact same thing with Dark AI thats why we don't have scriptable Dark AI commands its all about copyright that is also why there is no X10 source code so we cant steal the commands and use in other DBP games. Not all the shaders are like this but there are some hidden inside the source code which cant be changed at all. I felt like explaining that as i felt someone would ask the reason why it is done that way later on.
Pixel Shader Model 3.0 cannot be changed to work in 4.0 it just doesn't work, you must make it from scratch which when using the FPSC X10 engine is very hard to do that we have hardly any information on how the engine operates which is rather annoying to be honest. If we knew more about the engine then we could make custom shaders to a certain extent. FCV is correct FPSC X9 shaders DO NOT work in X10 it will crash the engine when you attempt to load it up.
Hope that answered all your questions as of yet. That should all be right it seems right but wrote this very quickly so if you find errors do correct me