It already has initials JW inscribed in the cartouche, though they are fairly worn, so I'll probably leave it as it is.
Interestingly those were the initials of one of my great-great-grandfathers (Jarvis Whitehead, 1834-1896) though I doubt that the box ever belonged to him. He was a Yorkshire steelman and probably couldn't have afforded such a box.
The box is about 75mm long and weighs a substantial 83g. Still feeling inordinately pleased with myself!
I tested it with some IHT No.22 (about as fine as it gets) - no leakage at all. I reckon that's remarkably good for a 170 year old snuff box. I have much newer ones that leak worse than that.