Question Re: Flexing
As far as I know you can't change the outer display of the time to something else.
However, like kipswholesale said, you can change the external display text (though only the text displayed when your phone is flipped open, not the time displayed when it's closed) by hacking a few files on your phone using a data cable.
This is the best site I've found with info on editing files on your phone, and has info on changing the outer LCD text:
Just FYI though, the V600 OEM flex which I'm using changed the outer LCD text from "Cingular" to "Motorola" w...
It's possible the hardware differences would cause an incompatibility, but that's one good thing about the way Motorola has seperate flexware and firmware. The hardware communication is pretty much handled by the firmware, where the flexware is just the software layer over it.
There will probably just be issues similar to using a V600 flex on a V400. Namely, extra software options for hardware which your phone doesn't have such as bluetooth or multiple color backlights on the external LCD.
I guess we'll see.