Mary, I'll give you my own thoughts on this, but I will defer to Henry on expertise.
Here's my thoughts. First off, you can apply another kind/color stain, but there are a few things that play into this scenario. Is the piece varnished/polyurethaned over the existing stain? If so this will need to be removed (i.e., stripped) to expose the actual wood. Stripping the varnish/poly will remove some of the existing stain, but some of the color will remain. At this point, and after roughing up the surface of the wood a stain can be applied (your choice of color).
Now if there is no varnish/poly, then simply sanding/roughing up the wood will allow for a different stain to be applied. But I strongly suggest experimenting on some scraps, because in mixing the differing colors you just never know what you'll wind up with. I do mix varying layers of stain on lots of projects (ask Henry), but I always test on scraps prior to the actual application.