Twin 4.7-inch mounts on War Emergency destroyers

Could War Emergency destroyers carry twin 4.7-inch mounts instead of single mounts?

Yes, if the ships were designed around them, probably with a slightly wider, longer, or larger hull.

Twin 4.7-inch mounts would need to be part of a War Emergency destroyer's design from the outset. The C-class and related ships might require a little more beam, length, or overall displacement to accept them. The change is described as modest, though it still affects the hull rather than amounting to a simple swap for single mounts. This short answer links gun-layout choices to the dimensions fixed early in destroyer design.