Hello and Welcome CorpsVet:
Yes, one man can replace the cable. The key to garage door work is to keep as much pressure as possible off the springs. Raising the door all the way is one easy way to relieve some pressure. There should be a place somewhere on the torsion bar to insert a large screwdriver or tire tool and let it rest against the door or ceiling; that being done, it should be save to work on. Keep in mind, the springs can pack a powerful whalop, procede with much caution. Semper Fi
Glennn