It’s kinda-sorta possible. First, ask yourself whether the mistake is going to drive you nuts if you don’t fix it. Leave it alone for a day or so, folded, and when you unfold it ask someone else whether they see a mistake. If they don’t, forget it.
Whether you can do this depends on the kid of yarn. If you have a little of it left, knit a little swatch of stockinette maybe ten stitches wide and three or four rows long. Purl four or five stitches in the middle so you can try this:
First, stick a needle through the stitches immediately under the mistake so they don’t get loose. Do the same thing to the row on top.
Next, thread some extra yarn–enough to go through three or four stitches on either side of the repair–into a yarn needle.
If there’s a back side to the work, turn to that side and pierce through three or four purl bumps before you want to start the repair. I mean actually go through the yarn, between the plies. If your yarn is thin and slick, tuck a very little bit of flexible stretchable fabric glue (it’s machine-washable) in with the new yarn. You don’t want enough to change the texture–just enough to help lock it in place if the yarn is slippery. thick, rough-textured yarn won’t need this. If the pattern and yarn are such that you can get away with tying and burying a knot, tie and bury one! Now pull the new yarn to the front.
Now take a deep breath, gulp and clip the original yarn beside the mistake. As you slide the new yarn through the correct way, pick the wrong stitches out, one by one. It’s sort of like Kitchener stitch. When you get to the other side of the repair, run through the yarn the same way and tie if you can. Clip off any extra yarn. The temptation to use the yarn you’re picking out is huge, but you won’t have enough to secure it without changing the gauge and making a more obvious spot.
This also works when there’s a hole, tear or dropped stitch because of a yarn break. It isn’t always perfect, but the repair generally holds.