If it comes to it, you can tint the rim instead of restaining. I use an eye dropper and drop 1:20 stain:isopropyl alcohol and then apply the resulting tint to the rim with a q-tip. This helps rejuvenate colour without requiring the whole pipe,to be restrained. This is particularly useful if you bleach the edge of the rim while removing tars with either spit or coffee. In both instances you are using a light acid to break down tars and remove smoke.
The method I use is to wet a tea towel and the place the pipe rim down on the wet towel for two minutes. I thennuse elbow grease and the towel to rub off the tars and smoke stain. True charring won't rub off, however, and you'll need to consider topping or reaming to get back to wood.
-- Pat