So instead of calling, I sent an email.
The question I asked:
I'm wondering if it's ok to let another member of my party take and use my MagicBand to access a FastPass+ if I decide I don't want to ride a particular attraction. I'd hate to have that FP+ go to waste.
The response I got:
Dear Larry,
We are pleased to learn that you are planning to visit Walt Disney World® Resort and appreciate your desire to make your visit as comfortable and enjoyable as possible! While we sincerely appreciate your request, this electronic mail department does not have the ability to access your My Disney Experience® account on your behalf.
MagicBands are non transferable however FastPasses can be transferred between guests that each have valid park admission. For assistance with your MyDisneyExperience account, please call our Internet Help Desk at 407-939-7765, option 3. Cast Members are available from 7:00 AM until 11:00 PM, EST, seven days a week.
For security purposes, we will ask for verification on all accounts we will need to assist you with. Please have the following information available for each account: First and last name registered to the account, e-mail address of the account and the address listed on the profile.
We look forward to hearing from you soon!
If you have questions or need further assistance, feel free to contact us.
Sincerely,
//Name Redacted//
eCommerce Sales and Service Team
So there you have it -- according to an official Disney email, FP+s can be transferred between party members, but MagicBands can't.
Again, are CMs confiscating MBs or blocking accounts? Not that I know of.
Will they let DGD use DGM's MB for a FP+?
What does the policy say?