Depending on how you plan to use it during and after planning. From my current understanding still of this app and site, the short answer is no, you can not combine. Something I asked about a long time ago and still have not seen that ability to join the individual trail information with simple distance and altitude where I have to manually (the chosen method of less time needed) or use third party to create combined trails (GPX, KMZ, KML type of file) that I plan to hike. I was told of a possibility in future. The only thing I can see currently with this project, is that you can go to create a trail section and draw a new trail on map if you know where it needs to go and try to trace existing trails you may use in area, although time consuming. That would be the closes way I can think of currently and you could probably save it as a draft and export the gpx file if needed from trail page. Again, time consuming method to draw hiking trails since they are not straight lines and may not be that accurate but give a rough idea on miles and altitude of terrain if needed.
For the most part if thinking for navigation, I do not use this or any other app as the main navigation on hikes (only ideas pre hike), most time things are not needed but map and compass (no batteries to worry about) are first choice where I use this app and another app at same time to track the hike with information of hike that way and photos from hike. I use two different apps to track on same phone for abilities provided by the app maker, but the readings are slightly different between the two for the same hike as well. If you are multi-day backcountry like I often hike, often no service and phone battery can drain quickly from more use even often while in airplane mode, so carry a portable battery for extra charge and use the phone wisely.