just open the folder containing the BIOS file then Right click on the BIOS file and choose Rename and give it a name like SLICBIOS.ROM That way it has an 8 character name which is DOS complient.
Obviously the modded BIOS file needs to be renamed so you can flash it from DOS and the name will be recognized by DOS. He probably left it named with the _SLIC.ROM that is added by the SLIC tool when the mod is done. I'm sure he did that so you could tell which one was modded. But, Since only you and the modder know whats in the file you downloaded you should probably be telling me this info.