The message that is shown when a member tries to change a family member connection on a PPP profile needs to be updated to reflect the fact that edits to children and spouses of PPP profiles are now restricted, not just edits to parents.
At https://www.wikitree.com/g2g/1097590/please-mother-gerritje-anthonyse-vanschayk-conraedt-teneyck a member who was trying to add a child to a PPP profile reported getting the following message, which I believe is left over from the days when only editing of parents was restricted:
"Sorry, you cannot add this existing person as a family member because their profile is Project-Protected. If their parents need to be changed, post in G2G. Follow the link in the Collaboration section of the profile and add the project tag."