if you use the stone, you can see a window appears with the improvement. first transfer the weapons which want to change the appearance. then insert object-a prototype of the lower rank of the first selected (or current). the obligatory condition in the fact that the weapons and the prototype should be of the same type (if you choose the sword - the prototype, too, must be the sword, if the bow - the prototype is also supposed to be the bow). select the button "upgrade" with some commission of adena. about d grade i haven't tested, but was able to through a similar stone from vesper buster change the appearance of the sword of miracles sorry for the russian official server screenshot, but see the icon of item and what is the weapon in the hands of my dwarf
this changes only the view of the weapon (in this case) to the same grade of lower. having grade d of that stone means you can change appearance only for weapons d grade (you rly have it? ;o). in order to change r grade item , you need r grade stone too. there's example on my armor: