Converting non-core provinces

I understand the penalty on non-core provinces, but wouldn't the conquered province eventually convert to a core province? From a gaming perspective couldn't this be accomplished by spending resources on espionage or maybe building some type of infrastructure? Perhaps the conquered territory could convert to a core province after a certain number of days or after meeting some threshold. They could even be core provinces of more than one nation.

For instance, in the 22 player map, if the Southern US were to take territory in Kentucky or West Virginia I don't think the citizens of those territories would produce at a lower level. If the Southern US were to take Philadelphia I think the citizens would protest more.

My point is that the current one-size-fits-all approach to territory "core" definition is broken and should be addressed.