I have stretched many calf shoes, but I have been really careful when trying to stretch cordovan. The grain is really tight in shell and they do not like to stretch. Shoe makers have to be careful when stretching shell over the lasts during construction lest they actually cause it to split. I do not know that you could generate that much pull with a shoe stretcher, but I would proceed with caution. I posted this video about a week ago, but it is applicable concerning the tearing while lasting up a shoe. Ignore it if you have seen it before.
No, not really. I tried a a stretch or two that were certainly not aggressive and I could not tell any difference. Is this because shell will not stretch? Is this because I was too timid? I just know I did not wish to run the risk of causing damage and did not pursue it.