out of box this works only via serial console, there is no framebuffer console enabled in kernel and the keyboard in not complete enough to enter commands (blue key would not work in pure console)

except serial console I see only one option in current state - compile custom kernel with mmc driver enabled, extract rootfs from firmware image to microsd card and boot such kernel with root set to mmc. then you can start xterm in clean system and fix stuff

or I think it is possible to prepare initrd image with basic stuff (dropbear over usb networking or even basic shell over usb serial gadget) and load and boot it via flasher

also before doing dangerous stuff you could have bootmenu installed and cloned your system to microsd card and either do such experiments there or at least boot from it in case you break system in internal flash.

Hmm, I guess it is time to try that initrd idea :-)