Instead of blocking out areas from the nav mesh, can I block it all out and then add small accessible areas instead?

Normally you add a nav mesh bounds volume to a stage, making everything accessible, and then add nav modifiers to block off certain areas. I want to do the opposite. I want to make the nav mesh inaccessible by default, and then allow the user to build paths across it. Kind of like sim coaster, where you are laying out paths around your theme park for the AI to walk across, or like the streets in sim city.

Is there an easy solution to this problem?

It looks like you can add multiple nav modifiers on top of each other, but the system always defaults to the nav modifier with the highest cost, which means that the Null modifier overrides the "paths’ or default modifiers.

Not that i know of.

Even using nav invokers you have to assume its all navigatable and block off areas on purpose…

I was worried about that. I may have to come up with another solution. Thanks.