Reskinning issue, beginners question

I am now able to extract eric_facemap.vtf from source 2007 shared materials and mess with it in photoshop. My question now is how do I get to the stage where I can use that face on a model in game? So far all I have been able to do is select models 1-9 for male and female citizens, how do I get my altered vtf’s to show up on this list when placing npc’s in hammer?

Also - when using these standard citizen models I find that they won’t remain stable. They either change each time I run the map or show up as different models to the ones I see in the hammer editor. If I cant get to a stage where I can use my photoshopped skins in hammer, I will at least need to ensure that the models available to me remain constant. Any ideas on this point as well?

Thanks all, really appreciate any help.