You can modify the 8 pre-defined layouts as you wish. The changes are saved automatically when closing Wwise. You can't however rename them.
For advanced users only:
When you change the layout, the changes are saved in:
C:\Users\USERNAME\AppData\Roaming\Audiokinetic\Wwise\Layouts\1\Modified Factory Layouts
You can backup this directory and create several layout sets. You will need manage which files are loaded by swapping files in the Modified Factory Layouts directory. Close and restart Wwise every time you change the files.