Possible to set user privileges on part of the text?
No, there are no ways to do this. And there shouldn't be. First of all, read PHP in database: bad practice but - this addresses exactly the situation you have here. Long story short: don't do it. Turn off PHP module if you don't need it.

And why you don't need it? Because there is Viewfield module.


  Viewfield provides a field that holds a reference to a View and renders it whenever the entity containing the field is displayed.


Exactly what you want to do, but without any snippets in user editable texts.