I haven't seen evidence that manipulating skee-ball machines is a common practice by owners, and I've played at a lot of places. Several of the modifications you mention aren't easy to make. (At least, I can say that's true when it comes to the official machines made by Skee-Ball Inc -- I usually avoid the knock-offs so I don't have much experience with those.)

I was saddened to learn that the company was acquired by a rival earlier this year and relocated production from the Philly suburbs (where it had been over 100 years) to Wisconsin. Strangely, no mention of any of this in the article.