I have tried this quite a few times with varying results, Re-spraying. By spraying a very fine mist of colour mixed into the same varnish you used on the wood. Mixing the stain into the varnish is the key here, by mixing a bit in at a time and testing on scrap wood. This takes time and patience as you must wait until the fresh spray has dried to see if it is the right colour or darkness. To get the best results write down every detail as you go. Example: spray test #3, 10% stain, 4 passes at 12 inches, colour American red oak minwax, polyvarathane fast dry varnish. You can get really good results if you take your time, but the best results I have found were achieved by stripping the piece down. Others here may have better solutions, this is just what worked for me.

I had thought of over coating but I never like how it hides the grain of the wood. My dad stayed he used a dye that he could go over old finishes with, but that was in the early 80’s Anyone ever heard of anything like that available now

I think that the chemistry keeps changing so much in finishes that it would be easier and faster to strip the old finish and do over. What might work today may not work in a couple months.

You could tint some oil and do a rub. It would take some time but it would do the job. Probably faster to just refinish