This is the link I used to get BIOS 302:
http://dlcdnet.asus.com/pub/ASUS/nb/GL502VS/GL502VSAS302.zipASUS still has the file up but no longer has a direct link.
You'll have to flash the BIOS using "other" methods as it normally won't let you rollback to an older version.
Aside from the obvious "BEWARE OF PLAYING WITH BIOS" warnings, after I used this ROM to rollback, my keyboard backlights went bye-bye.
After the rollback was done (and it stays on 302), I was able to reinsert my SATA SSD as a secondary and the laptop again booted to Windows. It sometimes hangs on Windows Updates that require a restart though.