Yes, it's possible, but first up I need to say that you should never use generated map data for navigation, especially through shallow areas! With a map created from consumer grade data, and depths interpolated over all of the areas without data points (this is most of the finished map area), it is simply not possible to know for sure that there aren't shallower (and potentially dangerous) areas in the map, that are not indicated because data in those areas was not collected. It is probably a better idea to record a track whilst running a shallow area in good conditions, ideally when the water level is low. Even then one shouldn't rely on the chart-plotter alone when navigating.
If you do want to add a track to a map, then you need to create a User Map from your map project (or create a new, blank, user map if you want it to contain just the tracks). You can then either import custom paths (from KML (Google Earth), GPX or Shapefile), or you can draw a path (or polygon) directly into the map. You can then style the path to make it more visible (line width, colour), and export it as part of the map. If you are exporting to AT5 or Google Earth, the lines will appear as they do in ReefMaster. If you are exporting for HB, you should probably create your lines in a separate user map so that you can style those tracks to appear differently to map contours.
Matt
