You could try MacGPX (the beta version, not the regular one) from here: http://www.javawa.nl/macgpx_en.html
The manual isn't translated yet, use Google Translat for that (or just try out yourself).
MacGPX isn't an editing program, but it can convert tracks or routes to courses and waypoints to coursepoints. The coursepoints will be attached to the nearest point in the nearest course.