I worked in a minilab one summer. The Noritsu printer had, IIRC, a +/- 1,2,3 override for R,G, and B. So if you saw a head over a big blob of green (someone wearing a red shirt), you'd hit +2 Red to override the printer's attempt to "balance out" the colors.
We never got any 'interesting' stuff. I suspect people would prefer a bit more anonymity than you would get from a 2-3 person shop where the person who printed your stuff might also be the one ringing you up for it.
My father owned a photoshop that was a one-hour lab for the last decade of its life. I worked for him throughout my teens and have printed many thousands of photos. I've seen interesting stuff. Most of it is pretty boring.
We never got any 'interesting' stuff. I suspect people would prefer a bit more anonymity than you would get from a 2-3 person shop where the person who printed your stuff might also be the one ringing you up for it.