Here's what I end up doing, ...
I use two lisp routines here. The first is crack, then specify a point that I want to crack the pline. In this case, midpoint. IF the pline is closed, it mearly opens the pline with the crack but you still have a pline. (Much like a closed pline rectangle). You can edit it and close if you wish. IF the pline is open and I crack it, it breaks the pline into two pieces. I then use the second lisp file, pljoin and connect the two together to have one closed pline. I then have a vertex or grip centered on the pline.
I came across a lisp file once that created a vertex anywhere you specify on a pline without breaking or cracking it, but I'd hardly ever use it so I passed it by. Can't remember just where I saw it at now.