.
Al least if it is not possible to do in 1.16.x ver., in 1.18 would be great for other users.

When playing with other mods that toggle the underground, the deepslate just replaces the stone, it's kinda frustaing.
A good idea would be, as the mod allows you to configurate everything in that big setting panel, to edit which vanilla underground generated stone blocks you want to get replaced by deepslate. <- That is the real suggestion.