Hi to everyone! I would like to say if it exists an unofficial firmware for my dvd burner who can turn it into a DL one, since the official fw is a year old now and does not allow it. So finally I may know if I have to buy a new DL dvd burner or not. Thank you.
I don’t think so, because you even not give us enough info…
Discinfo
I’m not quite sure whether it’s possible to crossflash your drive to a DL-capable LG GSA-4120B. I believe it’s not possible, but 4120 could be crossflashed to 4160… 
Maybe you should just get a LG GSA-H10N 
IF, then only +DL, not -DL, ever.