Having done much research about "font tweaking", I now came across this highly interesting similar "music tweaking" case, namely the music performance forgeries by Joyce Hatto, described in much detail here
http://en.wikipedia.org/wiki/Joyce_Hatto
and in dozens of other documents linked from this Wikipedia entry.
For instance, we read that the "music tweaking" (forging) of Chopin Mazurka performances was achieved thus:
"The CACD20012 release has added filtering, and the speeds of each performance pair vary slightly in the range of a few percent (+1.2%, -2.8%, and -0.7% for three sample mazurkas)."
This method of "music tweaking" (music forgery) is very similar to the method of "font tweaking" (Fred Smeijers).
At site http://www.creativepro.com/story/feature/21883.html we read:
"Smeijers introduces the term "font-tweaking," which he clearly doesn't think very much of, to describe the currently common process of simply taking an existing typeface and ringing a few obvious changes on it, then turning around and presenting it as a new design. Some of the results are simple rip-offs; others fall into a wide gray area - where does influence give way to plagiarism?"
see http://ospublish.constantvzw.org/?p=183 and similar sites.