First of all, welcome to this forum. I hope you like TG and stay here.

There's an input called final density. If you take one fractal (either power fractal or cloud fractal, with appropriate sizes and such) and plug this into each of those, you can alter all nodes at once. And of course you can mask this power fractal (PF) by other color fractals or other color shaders like a simple shape.

But beware that the power fractal is 3 dimensional, so not all cloud altitudes will change the same.

If you plug in a (blue node) constant color, you can alter density in an unvaried way from black (no clouds) to white (max cloud coverage).