Yes it is possible, but it's not going to be a fun job. Before sanding, I would try dipping a rag in paint thinner and then trying to wipe the stain off or just lighten it enough to be restained.

Wiping off stain alone does not make the stain look even. If the wood is blotchy, it could be stains from water or dirt that should have been sanded off prior to staining. Your floors look great because they were sanded. Also, the floor people should not get poly on raw wood...that's rude don't you think? At the same time, the painter should sand that off before staining it.

Many painters stain and do not wipe it off. Did you ask that the staircase match the floor? Of course they should have asked you that question before staining the whole staircase! Anyway, my concern is that they may not fix the staircase for free....it may end up being a lot of extra labor depending on how big it is. The end grains are going to be darker whether you wipe the stain or not though...nothing you can really do about that.

I ran into a very similar situation. DH was installing our hardwood floors (pre-finished with a warm golden>red oak stain). He installed new stairs and stair rail as well. When it was time to stain the balusters and railing I took a sample piece of flooring in, paint store called flooring manufacturer and got exact formula for the floor stain color. Another job I did fatigued (knew better, but with the major overhaul we wanted to hustle and wrap it up, the house was all torn up, furniture everywhere, etc.). I began applying stain to balusters in the evening without DH's halogen work light. Stupid. I had done half the 8 foot section before I went and got a really good work light and not only did it not match, it was baby poo brown. (Oddly enough, at the paint store on the sample baluster is was a near exact match). Getting that stain off was a bear and a half. I used a detail sander with multiple attachments (you can get one for about $60 or so and would urge you to get one, doing it by hand won't get all the curves, nooks and crannies sanded properly). There were deep crevices in the nooks and crannies that I could not access well, even with sandpaper folded. So I took some diluted bleach (1 part bleach to 3 or 4 parts water), applied to a q-tip in the crevice, let it sit, then sanded again. Not the greatest method, but it did bleach out some of the darkness.

I worked on that several days but ultimately got it back to where nearly all the stain was gone, just a light hue left. (Woodwork is oak, and being porous sucks stain deep into the pores.) I used Minwax Golden Pecan (a very light stain), added just a hint of the stain from the store, and was able to get a near perfect match to the flooring. There is a slight difference in stain between sections on the railing, but not readily visible to the eye. You have to know the history, and look closely, to detect it.

With the detail sander I started with 80 grit, then moved up in grit to 100, 150, 220 and then 280 or 300 for smooth as glass finish. The finer the grit, the finer it gets into the pores. I finished up with Minwax Wipe On Poly in Satin. It's been a few years and all is well. ;)

I was working on only 4 foot section and I would not want to do that again. If you're looking at a large staircase and paying someone to do it, it's going to be very labor intensive (and if you DIY might require more than one detail sander, meant for 'small' jobs, I had a motor burn up on my first one while refinishing an antique chair that had excessive details to be sanded.)

Oh, that little strip that came out lighter on the newel posts. You might be able to sand it off. Does sound like poly got on it and prevented stain from absorbing into the newel wood. If it won't sand off (start with grid order as mentioned above), you'll need to use a stripper (I like Bix Orange Get, doesn't splatter). But you'll have to be super careful and protect that floor really well!

Thanks for all the feedback!

I am at the same place where you were back when you posted this message. Can you please tell me if you were able to sand/restain the stairs on your own or if you had to get a floor guy to do it? I'm so upset with the contractor but I'm basically stuck with this ugly dark brown poo color on the stairs unless I do it myself.

Please let me know how it turned out. Thanks Jessie