Tweaking Shader Values in realtime

Is it relatively easy to tweak shader values in realtime. And if so whats the best method to do this, and what are the limitations. I would like to be able to tweak ambient, specular, diffuse, phong, tiling, etc. with a custom inteface i've built. What sort of variables do i need to make for this and how do I tie them all into the code?

Use material or entity skills. You can set mtlSkills in c-script with the float() function, and in lite-c by assiging a float value (like 1.0f). You can access these values in the shader with mtlSkill1...mtlSkill4 or the entSkill variables.

plus you have direct access to the materials ambient, specular and so on values thru vecAmbient ... in the shader