Hi Gazza. I tried to edit and add to the route. It did tell me to sign in before I could save.
I created an account. When I sign in I can edit but can only save to a copy in my account name as "This route is owned by someone else". There are options to share and make maps public etc but not played with this yet..
HerE is my test edit..
Hope
https://www.plotaroute.com/route/341228 that helps.
Steve