Don’t know how Lenovo has done your board’s bios updating(didn’t check). There probably is some kind of protections from updating modded bios. But again didn’t check.
I have my experience with different Haswell 2011v3 computer, which has not Broadwell support. But there is upgraded version of same motherboard which supports both processors.
I extracted Broadwell microcodes from newer board and also downloaded newest Broadwell one. I did try these with my motherboard and Broadwell Xeon CPU->no picture so there is something more than microcodes in my case. So I upgraded to 2696V3.