I reached out to
TME to see if they could contact Brymen about sending me a chip with the upgraded firmware for my BM867s that I bought from them back in August of 2018; Brymen told them no, that they could not send a replacement chip, nor could they provide any service that would allow for the chip to be exchanged for one with more up-to-date firmware. Maybe someone will have better luck with Welectron like Joe Smith did, but my guess is that Brymen has no interest in providing upgrades to firmware on existing multimeters to the average customer.
As an aside, using the technique mentioned above, the old firmware with the short backlight on the BM867s is also 869-P9, so this meter (naturally) shares the same firmware with the 869s. Does anyone have the firmware version number for the new firmware with the longer backlight?