Migration of Existing Image

[CVBruce]

I have a Raspberry Pi OS Buster installed on a USB3 connected SSD (240GB).
Is there someway I can get BerryBoot to adopt this image?
Can I shrink the partition of the existing install, and use BerryBoot to install additional OSs?

If my BerryBoot installation fails, is there someway to recover?

For example, assume the SD card fails, but the OSs are installed on an SSD. Can I get a new SDcard, install BerryBoot, and then use the existing OSs?

Thanks,