It sounds like from what you've said that you use the alex player in regular minecraft gaming -- maybe alex is the default character on your minecraft launcher settings? And maybe because of that, the player block in the 'create npc' block overrode the other part of the mod.
I'm not sure which block you painted to look like herobrine -- is it the steve skin? If it's the steve skin, and if you haven't already yet, try changing your default skin on the minecraft.net website to steve. (you'll have to login to minecraft.net) Or you may be able to do it on your minecraft launcher- I'm not sure.