Interesting question, and one that I've faced on a few occasions. The last time it came up, I contacted a colleague at the FDA and asked her the question. Following is a synopsis of her comments:
As long the requirements for medical clearance have been satisfied and as long as the technology is appropriate for the new fitting, there is nothing in the regulations that prevent taking a new impression and transferring the hearing aid to a different user. Donated hearing aid 'parts' are sometimes recycled, so there is no physical reason why this could not be accomplished.
All of that aside, the policies of the hearing aid company that made the hearing aid and the policy of the audiologist's office you are working with can vary. Speak with your audiologist to see if this option is available.
