I'm the OP. Thanks for all the replies. When I posted this question my concern was that I didn't want anyone changing routes I've curated. There could be "sharing permissions" of view-only and edit and it could work like a shared Google doc or Office file where people could collaborate and edit the file - that could be handy for trip planning, but I'd want the option.
Follow-up question, if I share a route today and a friend "uses" my route and copies it into their library, it's a point in time copy? If I change the route tomorrow the new changes will not be applied to my friends copy? Yes?
-Alan