What do you mean "switch back to 'normal' state of where it's at, AC or DC power"?
I've never used JEmplode to update my empeg so I could be wrong. No idea if Hijack will let you rewrite the Flash memory when on DC but the bootloader won't let you for certain. That's the problem you've got. I guess JEmplode could request http://your.empeg.ip.here/proc/empeg_power and parse that to work out what mode it is currently in. It would only work with Hijack but since you're attempt to update Hijack anyway it shouldn't matter.

- Trevor