A small table has a top that is very worn; part stain and varnish and part original wood. Can I only stain what has worn off?
It will be hard to get any stain to blend across the table surface without doing some work. It will be best to sand off the existing stain/finish and then apply new stain and finish. With that said you could do a light sanding and then rub a matching stain across the table top and see what it does. If it doesn't work then simply do a refinish of the table top.