Landscape: apply sculpt to whole landscape based on a mask

Hello, is it possible to apply a sculpt brush on the whole landscape based on a grayscale mask? Basically I have some areas of my landscape that are very pixelated, so I want to automatically apply the smooth brush on all areas of the landscape indicated by the mask (strongest smoothing value on the whiter pixels, none on the black pixels).

The grayscale mask is the same size of the landscape (16321 pixels width/height). The landscape is reasonably big and procedurally generated, so it’s impossible to do the smoothing it manually.