If you are woried about altering the dice you can leave them as is. I myself like to restore the dice in my personal collection. I find that the water based acrylic craft paint works well in logo restoration. It comes in metalic colors and washes off with water in the first few minutes so can be removed if you make a mistake or do not like the result. I always save a digital image of dice prior to any restoration or conservation measures to preserve a record of them untouched. You also have the option of restoring one of a pair and leaving the mate untouched. I do not restore dice I am going to sell or trade as some people do not like it. I do put a clear coat on all my nitrate dice to prevent them crumbleing away to dust.