Recent softmods don't load a BIOS in the way you're implying, so you can't change the BIOS. The softmod alters the stock MS BIOS in memory to provide all the features of a hacked BIOS, and so long as you used a good (new) softmod like Krayzie or Kingroach it will support LBA48, which gives you large disk support. Which softmod did you use?