After some trial and error, this has worked. (I'm currently flashing the original BIOS back)
I'm not entirely sure how, but, on an L480, I managed to get past the black screen issue after reflashing the original bios and then the patch again, at which point I could get to the lenovo screen. To enter BIOS options, I tapped the BIOS key (Enter in my case) right before the splash screen showed, as after that point it wouldn't work.