for me?
i have not done any staining of our tiles, but i have used a couple of products which put a new seal on the tiles. these were water-based products that i applied by just cleaning the tiles really well and then brushing on a layer and letting it dry. i have used several products and would not recommend a particular one because i'm not sure how the ones i have used would react with the seal you already have. my suggestion is to buy a small amount and try it on a small area. that is exactly what i have done. let it dry and set for a week 