No tickets need be attached to any particular MBs.
Tickets are put into a guest's MyDisneyExperience account and ANY registered MB that belongs to
a guest will automatically access any of the tickets in that guest's MDX account.
A guest can own any number of MBs and each MB can be used interchangeably with any others.
All MBs can be active at the same time and used for all purposes.
No changes need to be made for split stays.
Just to keep things as clear as possible-
There is no reservation info, or ticket info, or credit card info, or FP+ info "put onto" a MagicBand.
A MagicBand only contains a unique serial number that is used to access the information that is stored in a guest's MyDisneyExperience file.
When the MagicBand is touched to a "Mickey Head Reader,"
the MB's serial number is read and that number creates a an instant connection to the guest's
MDE account info.
The MagicBand works like the combination to a locked safe, or a key to a locked door.
The MB, itself, is not the container of the ticket or FastPass, or Room key number, etc.
The MB just
unlocks the guest's file of info, allowing it to be accessed from her/his MDX account when needed.