There are several layers of soles on the boots.
The first at the bottom is the sole most speak of, and the one which is susceptible to wearing out. It should be professionally replaced as it takes some skill, methods, and tools/adhesives to do it right.
Then there's the insert in front of the heel in the prev. generation of T6 and all T8s (BTW: kits are different - check B4 you decide/buy). It comes as a kit with adhesive and screws. This can be done by the consumer or a professional.
And there's a mid sole. This one is sewn in/sandwiched between the bottom sole and inner sole. Replacement is done by a professional as sewing/stitching. etc. is required.
The final portion of the sole is the inner, which comes in contact with and is closest to your sock/foot. Like the mid, it can be replaced and must be done by a pro.
AS farms out repair to a local (to them; they are in the south Los Angeles basin-bay - been there twice). If you call them, they used to refer to the local but last time I checked they were acting as a middleman. I have the name somewhere if you want it.
There is an other place in Escondito (sp?) CA which does excellent work in the $80 range. they have an ad in Cycle News. This one's contact info I have somewhere, if you want it. I would recomemed them as they use a better lasting sole from a competitor to AS.