I did it the hard way. In a nutshell:
- sand off all the factory finish from sole edge and heel;
- stain them with alcohol based tint;
- wet the leather and let it dry until moist;
- burnish hard with the appropriate shoemaker's tools until dry and nice and smooth;
- liberally apply wax of the same colour;
- burnish again with said tools, heated to almost 100 C°, to melt and push wax into the leather;
- buff with a woollen rag until shiny.
Quite a job, but rewarding as now my sole edges and heels are permanently stained in depth. If a little scuff occurs I just apply some more wax and burnish.
I am in debt with @DWFII as I used as a guide a shoemaking manual, wich he took the chore to scan and publish on "The Honorable Cordwainer Company" website some years ago.
That sounds like a great method, albeit involved. Still, sounds quite fun!