well, not all of those shops deal with electric motors--they're just good bike shops. You didn't say what you meant by "customization"--did you just mean adding a motor? if so, Easy Street Recumbents is the only good place I know of first-hand in Austin. You might want to check with RL Martin bikes too. Their stuff has been discussed a bit on this list before. I've never been to their shop, but when I've spoken to them on the phone they've been very nice (in strong contrast to a couple of conversations I had with a woman at Alien Scooters...).