There's plenty of tutorials on how to configure bt3 with saved changes.
IMHO, it's better to save only the necessary changes and keep clean all the rest so that every time you start your distro, it's always in the same "stable" state.
BTW, in order to have changes saved, it's enough for you that you type the following commands:
You can obviously call the .lzm file as you like, not necessarily "changes.lzm"..
dir2lzm /mnt/live/memory/changes changes.lzm
The reulting file must be copied in the "modules" folder under /BT/