This depends on the type of blending that you're trying to get. If you're blending the current object with other objects in the scene, you have to define those in the render states of the shader. Currently, the custom code node supports adding code the the header, the vertex shader, the pixel shader, and the input and…
Ah - cool to hear that ShaderFX is helpful! You can set the blend mode by selecting the standard material node and then choosing the blend mode you want from the drop-down box on the right that's labeled "Blend Mode." If you're making a custom FX shader for your artists to use, I'd recommend using three separate techniques…