In a leather braiding book by Grant, my copy is buried now so i can give youn a better citation, a method of softening rawhide lace is to take a short length of a large dowel, starting from the center of one end make a saw cut down about half the length of the dowel. Fasten one end of tne lace to something solid, insert the lace into the saw cut and begin pulling. By rotating the dowel you can cause the fibers in the leather to losen, and the rawhide is softened. Next work in saddle soap.
This is basically brain tanning, with the soap being a substitute for brain.