The most you can ever shorten a heel and have a shoe still balance correctly is 1/4". I've had heels completely changed and updated at Manolo Blahnik. Maybe Prada can do this as well.
How much was this service? I have a few pairs of heels I wouldn't mind updating; not sure if it would be worth it though
Just go to leatherspa.com, you can e-mail them and ask directly. I send shoes there all the time, they are the best!
You are amazing. I have been trying to figure out where and how to do this forever. Thank you!!