Is it able to flash bios on xbox - WITHOUT a modchip?

Yes, if it's a 1.0-1.5, but you can't flash a 1.6. It's called TSOP flashing, and you need to solder a couple of small bridges on the motherboard before you can do it.

you need a exploitable 007 auf or a mechassault. splinter cell works with the exploit also. do like he said bridge your points, put the save on your memcard (the exploit). boot, copy to hdd, remove memcard, boot up auf/mechassault/splintercell and flash away. if it PROPERLY DETECTS your flashrom you bridged everything properly. if you get a 0x09 flash not writable you didnt bridge the wires properly