tested with thinkpad x1 carbon gen 5 and openbsd 7.7.
this can brick your thinkpad! proceed at your own risk.

update thinkpad bios and logo

prepare bootable drive

# ftp -o - https://romanzolotarev.com/tp/bios.sh | sh -s sd2

bios.sh downloads an official bios update image, installs geteltorito to convert .iso image to .img, writes it to the usb drive, and copies logo.gif.

reboot and flash bios

thinkpad boot screen displaying a custom logo

image: thinkpad boot screen displaying a custom logo.

© roman zolotarev