[mk01]

@Jan,

in general yes, question is what version are you running now and how you created the usb copy.

for beta1X: if you removed subvolumes and adapted fstab to single subvolume btrfs filesystem, then the upgrade won't work (if you would insist on doing upgrade, then I can advise you how easily restore subvolumes). if you still have subvolumes, you should be ok. upgrade to beta2 should respect your root= setting in cmdline.txt and system itself is independent on actually booted root (in the mean of hard coded partition names/labels/uuids).

for alpha5: if general it should work. but this combination hasn't been tested.