So, here's an idea.... (just for the sake of discussion)....
What if the game's existing Population stat was renamed to something like.... "Nation Age". The current, constantly growing stat, presently known as "Population", would remain unchanged -- it would just have a different name. It would continue to be the legacy number that it has always been. And it would continue to be displayed (as "Nation Age") so that other NS players could see how old any nation is within the game.
Then.... add a percentage option that a player can manipulate (a toggle if you will, much like the "issues per day" toggle behind the scenes). This percentage toggle would apply a superficial chosen "population modifier" to the NS population stat (renamed Nation Age). This modified result would then be listed (alongside the original nation age of a nation) in the new wikipedia-like boxes on our nation pages, any other population reference on nation detail pages, and would become that nation's new player-chosen public "Population" statistic
On the most basic of levels, the only thing that would need to change is the current "Population" stat being renamed "Nation Age" in-game. Nation Age continues to grow as it always has, and players can control the publicly displayed number that lists their national population. This keeps the current game infrastructure, while allowing players to have a little more control over the listed stats that publicly define their nations.
And I imagine these would be remarkably simple adjustments to make -- since they are both superficial.
Problem solved (while retaining "the way things have always been done").