@ianmedium
Yes, when he says reshell he means that they disassemble the casing of the original IEM and take the innards - the drivers and crossovers and such - and put them into custom shells. They are not sleeves. Once you've reshelled, there is no going back.
The biggest benefit is the fit. The fit in and of itself can bring paramount wonders to the sound. Also, since there won't be any tips, there won't be an extra layer of coloration to the sound that the tips present. All of this is only true though as long as the company that does the reshell stays true to the original design and layout. Also, the comfort will be in another world than what you are used to. Customs feel so much better than standard tips. Depending on your ears and the custom's build quality, you may be able to wear them 24/7 and even sleep with them on! (I suggest letting your ears breath though lol)
http://kozeesolutions.com/product/42/universal_reshell
That is the place that I've chosen to reshell my Triple.Fi 10. Their president, Adam Palmquist, has to be the nicest guy I've ever met, and he will assist you and answer all of your questions. If you look through a few threads here, you will see that their quality appears to be top notch. Also, I think the forum member "average_joe" said something about Kozee possibly being able to slightly alter the sound signature to become closer to one's personal taste.