Years ago, I used to have my own patch for Window Maker, that I never released. It used to have somewhat different images and rendered the active window's resizebar different from those of inactive windows. I applied my patch on every new release.
These days, I am too lazy to be a pixel-perfectionist and install from source -- I use the stock Ubuntu package.
I also had my own GTK theme (for Gnome apps), back in the 1.x days. This I did release, though, and it was somewhat popular. It did not only draw things to fit with Window Maker, it also patched the code of some existing widget classes to work in what I thought was more usable. It was quite a big hack, indeed, all for perfectionism. I even had my own graphics routines to draw antialiased arrows and tabs in user-selected colours. When GTK had a large internal redesign, I didn't rewrite my code, so then the project died.