If a profile is on your watchlist, you can change it.
If your profile is on someone else's watchlist. They can change your profile. This only would happen if you added them to your trusted list.
To find your watchlist. Go to My Wikitree in the upper right corner (drop down menus) Second to last item.
To find the Trusted list of a profile, click on the tab at the top of the profile that says "Privacy"