Yup, you can use the usb-gadget mass-storage framework to "plug in" a "block device" which is backed by a file on the computer. You can then "unplug" the device

Yup, you can use the usb-gadget mass-storage framework to "plug in" a "block device" which is backed by a file on the computer. You can then "unplug" the device from the usb, and loop-mount it locally to manipulate its contents. Nota bene, do not mount it two places at the same time!