I have altered several of these but the ones that go over the best for me are the Birthday tins, I've left a link below.
I think the most wonderful thing about altered anything is there are no rules...you just fly by the seat of your paints and do what you like.

I used a base coat to paint the whole tin usually in a low metallic silver, or black then work from there.

good luck,
ginger

Here is a link that might be useful: My First Altoid Tin