1. The first thing I need to know is how to skip the first record in the input file.  It just lists the names of the data in the records to follow, like PROLOGUE.  The output file does not have an equivalent line - it just starts with the records of data.  So I want GPSBabel to recognize the first record as a PROLOGUE but then just throw it away in terms of the output.

Is having that header line harmful?  We don't allow having a different PROLOGUE on input and output.

2. The Date/Time data in the input file is very similar to the GPSBabel field LOCAL_TIME.  I haven't yet checked out strptime formating, but it is likely that this would work.  Help would be appreciated.  Note that the input data does not specificy the time zone.  But I will always be in -0400 (Eastern Daylight Time), so that can be assumed, I guess.

It's not clear which of the two you're asking about.   The strptime/strftime conventions are pretty well documented.  At a blush, I think you have "%D %T" and "%v %T".


3. The date in the output file appears to be in ISO_TIME format.  Note that the Mac csv files have a space separating the time from the time offset (-0400).  Will that be added automatically?  Also, since the input files don't specify the time zone, then can I just add a constant (" -0400") to the output field to make it right?  Would that be an OFIELD CONSTANT?

..only it isn't actually a field, it's PART of a field.  You can probably play games with the "suppress field delimiter"

But TZ offset is simply %z


4. Finally, the Mac user interface GPSBabel+ is very handy to use, but I don't see how to use styles with it.  Can styles be specified using that easy interface?  Alternatively, I can write a simple Applescript program that calls Do Shell Script, which lets me run the GPSBabel program directly.  It would be a nuisance to have to go into Terminal every time I wanted to convert a file.  And I would rather not implement C compilers on my Mac.

You don't have to "implement C compilers", but you can't do it from GPSBabel's GUI unless you rebuild GPSBabel to include your new style formats.   Front-ending GPSBabel with Applescript is very common.See http://www.gpsbabel.org/os/OSX_AppleScript.html for examples.

If you send the completed style definitions along with a paragraph of doc and a test case, we'll fold them into the main tree so they'll be available in the GUI and there for the next user.