Fubar,
When I first attempted to make "something" out of my rendered fat, I was going for that type of product. I wanted a string wax / bow wax / boot wax type thing but it didn't really work out. If it is stiff enough or waxy enough for string wax or bow wood protection, it's generally far too stiff to use on leather. I thought a while and came up with the idea to use my "secret ingredient" which is another very old time product and it worked great. I can vary the ratio and get different consistencies but have settled on something that is real good for all around use. It is pretty stiff as it sets up in the tubs but like shoe polish, once you "mush" into it, it's pretty creamy. I'd describe it as being harder than room temperature Mink Oil, about the same as shoe polish but it feels different once you mush into it.
As for using it on strings, I really don't know how good of an idea that would be since it has animal fat. I don't THINK there would be any problem but I just don't know.