Ken and all,
Yes to both questions. When applying over an existing finish, my attempts have been with oil type finishes vs. paint (varnish, polyurethane)type finishes. However I have had good results with penetration over Tru Oil or Permalyn modified oil.
I have never applied full strength over bare wood as I fear this would leave a mottled mess. The product is quite concentrated and thinning would be the prudent first step for bare wood. For bare wood I tint boiled linseed oil to taste and apply, the coloration is more progressive this way more akin to alkanet with a little help. At present I have an oil with both alkanet and Blood red so I won't miss the stink of the alkanet. Be aware that when using Behlen stain that is dries quite quickly.
When overlaying an existing finish I use a 1" foam brush and keep it moving so there are no drips or lap lines. Let dry and wet sand with oil and 1500 grit wet/dry or lightly steel wool with 0000. This should give you a pretty good idea of where you're at for color. I know it sounds like alot of hoopla but you really can't go too far wrong and you can tune the finish as you go.
Anyone that wants more info can PM me and I will share all I know. Let the Englishmen laugh, in the next thread we can talk about how to put cup holders on your double so you can keep your drink close at hand. It took them close to 2000 years to get where they are, we did it in a tenth the time and we're only short a few nice churches, a couple dozen castles and Shakespeare. I hope I didn't forget anything else, but I'm in a bit of a hurry.