Version 0.2 is now available. This implements the pngcp command, which can be used to edit the characteristics of PNG files. You can download the source from here.
A historical note from November 2020: this code is quite old, but still actively used. I have therefore converted the old subversion repository to git and it is hosted at https://github.com/mikalstill/pngtools. I will monitor there for issues and patches and try my best to remember what I was thinking 20 years ago…