Our daughter has a codman reprogrammable vp shunt, and we also received no information as to the possibility of accidental resetting of the shunt. My husband found information regarding this on *edit*
This site contains information that magnets greater than 80gauss strength may affect these shunts. Eg toy magnets are approximately 100 gauss. Rare earth magnets such as neomydium are over 2000, and these are use in earphones, computer hard drives etc (see wikipaedia)
Contact with Codman also alerted us to the use of mobile phone close to site of shunt, and caution with metal detectors at airports.
Seems to be essential to do ones own reearch...so much for "informed" consent