While, yes, you can bypass using Kiosk Firmware, you still cannot place previous updates on your system.
For example, if I wanted to do the Prestige Glitch on Black Ops 2, I couldn't just delete the patch and do this. It will not let you on. You have to install a previous patch (1.04, for example), then do this.
The previous method for going back to a previous patch has been, you guessed it, patched. I'm trying to experiment with blocking Sony IPs to see if that will work, but my currently bricked PS3 is hampering my progress.