Ok idea, or very bad idea?

I ordered a neck from Warmoth finished in Satin. I was toying with the idea of sanding the face of the head so that I can do some dying to it to match the body. I want to keep the rest of hte neck completely as it will come from Warmoth, just wanted to add some color to the head.

Any recommendations on how to do this or should this be avoided at all costs.
Very bad idea.  Very very bad. 

The finish has a good chance of peeling, coming of the maple at the edges of the headstock.  You're going to have to refinish it in such a way that the new finish is going to look right with the existing finish.  I'd nix THAT idea.

What you CAN do - if you're good -

You can overspray the face with lacquer.  Then you can add a toned/dyed/colored lacquer over that.  Then clearcoat over that.  That will preserve the original finish.  It will also allow some removal of the toned lacquer since its clear lacquer under it (keeping the color off the existing epoxy finish). 

Check with Warmoth to see if their finish can withstand a lacquer overspray.  I'm pretty certain it can since its a catalyzed finish.

If you decide to go that route, you can wet sand the face with 600 grit to knock the gloss off and give the lacquer something to bite onto.  If you decide to just say forget it after you start, you can remove the lacquer, and buff out the 600grit sanding, and not be too much worse off for it.
According to Warmoth's website they use polyurethane, and occasionally use polyester as a base coat.  I would recommend applying 2 - 3 coats of wax free shellac prior to shooting any lacquer, just to insure you don't have any compatibility issues.

You didn't state what wood the neck is, but if it's rock maple, you might have a difficult time getting any stain to "take".  Warmoth states a peghead requires a maple veneer to stain.

CB's idea would probably be the way to go, just add the shellac step.