Brian,
What I will write you is what Spada was doing 2 years ago and as I said already they are constantly changing and improving their services. When I went to buy my trumpets you could test differents bells, leadpipes and tunning slides. As far as I know, at present they are not only customizing bach trumpets, but also building their own brandt of trumpets. They were customising mouthpieces too, but this service was rather limited. The most popular was to take a bach rim (or cup: not sure what is the right term in english) and screw on it a schilke backbore because of his larger size (mainly for orchestral playing). The best thing to do would be to contact them through their website at
http://www.spada-music.ch/seiten/start_1.htm and ask them what they do at the moment. Though the site is entirely in german you can write to them in english. Hope this helps.