Question RunTime Modifications On Surface Area

Hey!
In my game you pay money to unlock new pieces of land. I can't rebake the whole NavMesh map everytime a land unlocked.
I tried to assign "lockedArea" to lands which is locked, "unlockedArea" to ones unlocked.
I unchecked lockedArea from my agent's area mask so agent couldn't go there. It works okay.

But here is the problem: when i unlock a new land i change land's area to "unlockedArea" via the NavMeshModifier from code, but agent still assume it is locked.

I can't rebake the map over and over again since it is a mobile game and it causes huge fps drops.

So i need to update the navmeshdata somehow. I would appreciate any help!