I don't know if the soap will damage the insulation or not, but it will set up like adhesive when it dries out. I have a friend who is also an EC who used to always use dish soap for pull lube. When trying to remove conductors from a conduit to reuse the pipe after a couple of years he found out just how well dried soap works for an adhesive. 10 #12 stranded THHN in a 3/4" EMT run of 250' would not break free.
