Ed knows a lot more about these radios than I do, but I'll offer the info I've seen posted about this.
The radios use the same module but you will not be able to take the module out of the 9C and use it in the 8 once it's formatted for the 9C. I'm guessing you'll be getting the 9C Super and you can't go back and forth between even the regular 9C and the Super.
When you first plug in the module to the 9C, it will say something to the effect that it's been recognized and ask if you want to format (or something like that) the module. You tell it yes and I think that will erase the models stored by the 8.
Maybe Ed will chime in again with better information for you...
Oh, the spell checker did not work when RCU migrated to new servers. The button was there for a few days but the spell checker didn't work, so I imagine they just dropped it since it wasn't working. Whether or not it will be back, I've not seen anything posted about it not working, it's disappearance or whether or not it will be back.