Yes, it sounds like you're describing the old-timey effect of saloon pianos, badly out of tune ticky-tack uprights, etc. (The sound of Keith Emerson's honky-tonk piano in "Benny the Bouncer" or "Bitches Crystal" come to mind, among others.... I think that may have been a special piano made in the UK - at least the one he had on early tours in the 70's for the same sound onstage...)
Thumb-tacks are of course the most radical and less permanent way to do it in a studio, but I wouldn't dream of doing it to a "priceless Steinway". (Not anymore! ;-)
Many years ago, I wanted to brighten up my old spinet, and a piano tech showed me how to apply a thinned-out coat of laquer to the sides (shoulders) of each hammer. But it's tedious, (gotta use a hypodermic needle to do it properly), very time-consuming, and not easily reversible if ya don't like the results.
For all the time & trouble of mucking around with a good piano (and risking some real problems afterwards), you'd do better using a sampled "Honky Tonk" piano, maybe even with a li'l bit of flanging & chorusing.