K850, very small firmware modification needed :)

Hi :). I'm really sorry for my bad english, hope you can understand everything i say :/
I've sent my phone to service to repair the touchscreen problem. That's fixed, but i got another problem, which is their fault. They have somehow damaged the background keypad light, and now only the bottom right part is lit, which looks awfull. Since i can't go back there where i've sent it to repair (don't ask why...), i was thinkig of a firmware chabge which will shut down that backgorund light totally, but there comes another problem, i don't know how to do it myself. I know how to flash a phone, but i don't know how to modify its software.
I've seen many modifications to that backgorund light (it can flash, flash certain parts etc.), and, if it can be modified, probably it can be shut down completely.

So, i'm asking: is anyone out here capable of doing that (im 100% sure there is :) ), and does that person have the time and will to do it?
I didn't saw any thread about this, so i'm asking here. Big thanks to everyone who helps me in any kind of way :)