I must be really lucky because I replaced 6 grip shift cables on a bunch of kids' dept. store bikes not long ago. My main issue was finding the varied position on different grip shift models where the cable head actually threaded through. Some were tucked under some rubber flap of the twist mechanism. Some on an inside edge of the shifter facing the brake lever clamp. But in all cases, I was able to thread the cables back in no problem. I think the reason was that prior to running this repair workshop, I got a cheap soldering iron and just melted a little soldered one the cable the tips of a few new derailleur cables and then pinched the tips to make them sort of pointed but no overly so. This really let me push around inside the cable routing path and not worry about causing the end to bend a strand off the cable.