"Spiffy new hair packs?" Are these like Apachii Sky Hair and MTOH?
When I create one, I just make sure that plug-in .esp or master is checked in the data menu but not the active file. The active file is your mod.
I then create my NPC, and the hsir plug-in will be available as a choice for hair.
I specify in my release notes for that esp that the hair pack I used is mandatory, or the NPC will appear bald (unless it was a replacer, in which case it will just appear differently).