It'd be great to have them supported too. Sadly, because they are created before y'all loaded, gonna have to either list them manually, or loop and match. This worked for me:
for name, tile in pairs(data.raw["tile"]) do
if name:find("refined%-concrete") then
tile.variants.material_background.picture = "__Concretexture__/grid/concrete.png"
tile.variants.material_background.hr_version.picture = "__Concretexture__/grid/hr-concrete.png"
note: gotta escape the - because find is a lua pattern, and patterns treat - as a meta-character. -_-