You can edit any profile that has the Edit button on it. It would be preferred to add Sources with anything being edited. If you are going to make relationship changes, it can be advisable to send a message to the PM unless you have clear sources stating the relationship.
For profiles that are Project Protected, you have to be a little more cautious about what types of editing are being done, but you can also leave a comment on the profile mentioning the source and information that you want to add. You cannot add or change Relationships on Project Protected profiles, but you can leave a comment on the profile with the information.