Can luster dust be added directly to royal icing and have a gold effect?
I think it depends on how much you need! If you want a really VIBRANT gold... I'm not sure adding the dust directly to the royal icing would give you anything other than a muted yellow/brown ish color!
if you're just doing accents with gold, perhaps you can pipe your royal icing, let it set up, then paint on the gold accents with a mixture of your gold dust and vodka. the combination makes a nice 'paint' which is perfect for adding touches of brilliant gold color. There is also a can of gold, edible, spray paint... usually available in most cake supply stores or on line. I have just added a photo that has some vibrant gold accents on it!
I have fine detailing to do on a cookie and I'm afraid painting over the RI with the vodka mix will be messy.
If you have a small enough paint brush, and mix... your vodka & dust to a consistency that's thick enough.... with a very steady hand, you should be able to do it!!
I would try to pipe some RI on a piece of paper and do some practicing first!
I looked at your photos... you're very talented! I'm sure you'll have no problems!!!