| Maybe. It depends upon what is on there now and your proper choice of products. Stain, by generally accepted definition, is designed to be applied to bare wood. The wrong choice of stain or finish from the home center could spell disaster. The process you are describing is glazing. A glaze is a color product applied between layers of finish. The difference is more than semantic, because you must choose the proper product for a glaze. Confusingly, one such product is a GEL stain. There are also glazes that are specifically formulated for this purpose. Once you apply the glaze and let it dry thoroughly, you need to apply a top coat compatible with both what is there on your cabinets and what glaze you use. You are not likely to find this type of help by anyone wearing a bright-colored apron or vest, if you know what I mean. I can't really tell you where to look to find product help as it's hard to predict in your neighborhood. There are a couple of independent paint stores around me that if I walk in, they greet me by name, and when I ask for oil-based VanDyke glaze, they ask now much, and don't give me a glazed (pardon the pun)look. Glazes are pretty easy because they are designed to be manipulated so you can adjust it by manipulation until it's to your liking. If you don't like it, you can wipe off and start over. The finish that is on there now is highly dependent upon when your cabinets were made. Many are lacquer, a lot of those are pre-catalyzed lacquer. Fortunately, for a vanity-sized project, you can probably get by with a few cans of aerosol of either of these two products (again from a paint store that caters to the professional finisher.) But more recent choices can be post-catalyzed lacquer, two-part finishes, other finishes that will defy another finish from adhering well to it. Just "slapping on a coat or two of polyurethane" is unlikely to be successful. A whole different option is toning. This is a finish with color in it. These normally need to be sprayed to go on evenly (Read: forget Polyshades). Again, you can find these in aerosols for your small project. But toners are less forgiving. Very, very, light coats sneaking up on your desired tone. It's very quick to go from too little to too much and getting too much color or opacity before you know it. While you don't necessarily need to apply a clear coat over a toner, it's a good idea. One problem with toners is that if it chips, you end up with a different colored (lighter) spot. You see this a lot on low-end furniture where the finish is entirely toners, a chip and you see bare, uncolored wood. Another wrinkle in the whole idea is the vanity end-caps, if any. These are often just a vinyl laminate that approximates the wood color. You can't really do much with these except to cover them with real wood. Whatever you decide, I'd recommend practicing / trials on the inside of a door before you commit to front and center. | 
