There should be no problem mixing gel stains. But to be safest, use the same type of stain from the same manufacturer. I regularly layer stains and glazes to get the color match I want.

If you want to rough up the finish then apply a gel stain, what you are doing is glazing. You will need to recoat the stain with a compatible clear finish to lock it down.

Here is a link that might be useful: coloring wood

kmealy, thank you for your response and for the very helpful link.

so THAT'S what glazing is! with the clear finish, do you think it will be durable enough for kitchen cabinets?

thanks again..

Be sure to experiment on scrap pieces before you hit the cabinets. I've used gel stains and my experience is that they look best with just one coat, but with each successive application the wood looks more "painted".

I wouldn't "rough up" the pre-finished surface before adding gel stain. If you sand through to the wood that area will "take" darker, and the uneven look may not be what you're after. You could instead use a liquid deglosser.
I used gel stain on my unfinished cabinets. I was very easily able to get a glazed effect with two coats. I used Bartley's brand. My case was a bit different because I applied pore filler over the new oak, so that acted as a sealer to prevent the stain from soaking in. On bare wood, if you work fast, you may be able to get it in one coat. Bartley's gel stains dry very fast, you do not get a lot of working time, doubly true on bare wood.
The Bartleys gel varnish is also a good product.
Casey

The idea of running some test panels is a good one. It's sort of a cardinal rule.

Be careful with your top coat over existing finish. In the last 10-15 years, cabinet mfr have been using a lot of 2-part conversion finishes on cabinets. These are generally very tough, but not agreeable to repair or top-coating with anything. It can range from splotching to not adhering well.

Oil-based gel stains will have a longer open time if you add a little mineral spirits (1 teaspoon per pint).

For good information on glazes, see either Bob Flexner's "Understanding Wood Finishing" (2d ed.) or Jeff Jewitt's "Complete Illustrated Guide to Wood Finishing." Both have good information and lots of photos.

Sometimes the glaze is left to "hang up" in the moldings, corners, and details. Other times, it's applied to add depth and adjust overall color.

thanks all, for the additional advice. i will experiment like crazy before deciding on how to procede.

Yes, you can mix and layer gel wood stains. However, you should always test your stain mixture on a small, inconspicuous area of the wood before applying it to the entire surface. This will help you determine if the colors are complementary and if the finish is even. More details I found here.