Reefmaster Waypoint Manager allow you to Split a Trail into Trail-Segments.
How about functionality to Merge Trails back into a Trail with Trail-Segments?
And I purpose RWM import and export Trails and Trails w/Trail-Segments using the following Google Earth structure and have attached KMZ and the expanded KML as examples of a lake with submerged roadbeds.
RoadBeds as Individual Trails.KMZ has the <Placemark><LineString> under <Document> where <Placemark><LineString> define each individual trail.
RoadBeds as Trail w/Trail-Segments.KMZ has a <Folder> under <Document> where each <Placemark><LineString> defines each Trail-Segment. Trail is the <Document><Name>
In a nutshell, any <LineString> in a folder or subfolder is a trail-segment.