The tool was only for windows though, but he provided the source-code, so I tried porting it to build for Mac OSX (to work on my macbook), so I'll share that effort here, just in-case other Mac users might need it:
If the PETSCII character is A-Z, make it a-z (PETSCII 97-122, subtract 32) If the PETSCII character is a-z, make it A-Z (PETSCII 65-90, add 32) If the PETSCII character is 192-223, subtract 96. Then subtract 32 if the resultant value is 97-122.
And here's another fun trick:
A group called "Style64" has created a TrueType font that maps the PETSCII character set both as screen codes and in the PET ASCII order:
If you add the PETSCII value and $E000, you'll get a Unicode character that matches the PETSCII symbol. You can then write that back out as Unicode text and load it up in a text editor that can handle Unicode.