How do I change the UEFI Boot Order from within Windows 10?
This is not documented anywhere by Microsoft. However I was able to look through the source code of Grub2Win to see how they accomplished switching order.
Aparrently there is a bcdedit object called {fwbootmgr} if you change the display order of that item, it will effectively change the Boot order within the UEFI.
bcdedit /set {fwbootmgr} displayorder <ID_OF_NEW_OS> {bootmgr}
You can get the id of the other UEFI entries by doing: bcdedit /enum {fwbootmgr} and looking at the boot entries under displayorder.