Using partial normal maps for character wrinkles I can't seem to find any solid way to do this online.  I'm trying to have wrinkles on skin during animation.  Baking a static normal map on mesh will not do the job because I only want certain areas to have it and I only want it during animation.

Perfect example is:

https://www.youtube.com/watch?v=4aRPr7ftUgg

Thanks for your help.
You can animate shader values like any other property in Blender.  Just right click and insert a keyframe.  Or, for better control, add a driver based on an animated control.