Enforce base ruleset

We are using SonarQube 7.1 and we would like to create a standard ruleset and enforce it for all of the projects. However, the projects should be allowed to add their custom rules on top of it without being able to change the base ruleset. The issue right now is that when projects are inheriting the base profile, they are still allowed to change the parent and therefore circumvent the use of it. What can we do to disable the option of changing the parent? Or is there any other way to achieve this?