The presser foot shaft orientation is held by one screw. But there is more to it than just loosening the screw. On a 401 there is a height above the needle plate measurement as well, and there should be some movement of the presser foot lift lever when it's down. This is so the spring is actually putting pressure on the presser foot, not on the lever.
Yes, you can do it if you are mechanically inclined. I would suggest you download the shop manual from the Singer site. I'm afraid I don't have the link to that file though. It was on my old HD when it failed. All I have left is the printed copy.
Joe