Recommend using TopoFusion for this. I believe the trial version would work, but it’s a great program created by a fellow AZT’er and I recommend it heartily.
Assuming a thru-hike, import all of the individual passage tracks in TF, merge them, simplify the whole thing down to 10,000 points, then split into 20 tracks of 500 points each, which is standard max capacity for a GPS unit.
This way you get to carry the entire route at once without needing to import more data during the trek. 10,000 pts on an 800 mile long trail should still be sufficient detail for occasional nav / confirm.
blisterfree