errr... they are Protestant/anglo-saxon already...
I wouldn't say that the Alaghenny territory, in EU 2 terms, would've been mostly populated by 5 Civilized Tribes at the time.
and it was a popular notion long before 1830... It won't make much of a difference in the game, except confuse the hell out of the AI or human by having WAAAAAY too many events clustered around 1835.
That doesn't mean that in 1821, the US could say California was a national territory. That's absurd. It would've been a painful rationalization for war at the time.
Like I wrote earlier, I think the event should be triggered by Polk's election, since his political astuteness (specifically, in provoking a Mexican attack, so he could have his propaganda victory) that allowed for relatively little domestic disturbance.