Convertible's interior roof replacement question

I have a quick question. While my outer top (original, I believe) is still in very good condition, the headliner has some minor mildew and weathering stains, etc. Also, the dampening/insulation material between the headliner and roof top is clearly decaying (pieces of it are flaking off and falling into the cabin quite regularly, and it all sags rather heavily against the headliner material).

Is it a ***practical*** task to consider replacing those two items (headliner & insulation material) without having to remove the outer top as well? Or does doing any of it mean doing *all* of it?

Dennis Rainwater @drizzle