So my first question is just exactly what does the PP do?
In the Vectric software, when you create toolpaths, these are basically stored as moves from one point to the next using the X,Y, and Z start and end points. The software also notes whether this as a rapid move or jog where no cutting is taking place, or a regular cutting move. It will also track arc moves.
As you correctly noted in your description, when you save the toolpaths using a particular post-processor,
it writes the header information
it combines the information from the toolpath operations and maps it to the specific machine commands, if the machine doesn't support arc moves then it translates those arc moves into many short lines to form an arc
finally it writes the footer information to shut down the cutting operation
I've read the help file on editing a PP in the help section of the software. Can I take a working file from our system at work and copy in the needed header/footer info into the edited PP?
That is a reasonable starting place. The same applies for the footer information.
Proceed carefully and try to understand that each command in the header and footer is doing.