Thedead1440 beat me to it, with the link to that post. Without trying though my first guess is that replacing the ttf files with others, even with the same filename might not work (due to 5a in the linked post), but it's worth a try. You'll probably have to delete Nokia Pure altogether from /usr/share/fonts if it's going to work.

The correct way to tackle this is to find the css declaration for the fonts which I assume it should be included as a constant, not declared many times. Ask a theme maker, s/he'll probably know.

Another more hackish way if the previous one doesn't bear fruit is to open your font in fontforge, change the name to Nokia Pure, rename just like the font names in /usr/share/fonts/nokia/Nokia Pure and replace. This last solution will most probably work, but if your font has significantly different metrics than Nokia Pure you might notice texts off-center (or even off-container) in some complex ui structures like the timepicker or the dialer.

PS. I still run the PR1.1 font in PR1.3. That method still works. However in that case both fonts are named Nokia Pure.