llRotateTexture?

I am working with creating the effect that a flat prim is rotating and I've tested and I've seen that llRotateTexture works quite adequately. However, I am not sure how to limit the texture rotation to only the top of the flattened prim. Could anyone offer some clarification on how to do this?

Also, is this the easiest method, or would it work better to rotate the prim as a whole? If so, how would one do that?

It would be better to use one of the client-side effects: llSetTextureAnim for just the texture or llTargetOmega for the whole prim.

You can limit the texture animation to only one side with the integer side argument. Look here to determine the correct integer to use.