Err thats not slim thast just (r)sl*. The pixars manual, go to www.pixar.com and log onto your account (if you won prman you have a n account ask your boss/school etc, or ask them to make a local copy of it), is quite good theres a sl reference for prman spesific extensions.
Tough sl is quite well documented in general on the net just search for the renderman specification, but not as specific as the prman manual which applies to prman only.
Slim is code to write code, the idea is that slim tcl wraps around the sl code so that the ndoe connection can inject your coede into other partial shader parts.
Basically change the ci line to:
Ci = diffuse(faceAxis) * alphaGain * mix(afterNoise, afterCondition, conditionColor) +specular(N,-I,0.3) - Os;
Change 0.3 to something between 0 and 1
PS: best normalize N and I