I know there are several security settings in Project Server that deal with Windows SharePoint sites for projects in PWA. They are called Manage SharePoint Foundation, Contribute to Project Web App and Manage Lists in Project Web App. You could give it a try and see if it pertains to what you are trying to do. The documentation that I have here is pretty sparse on the subject, but the security settings for project sites are synchronized with Project Server, so it is likely the control is actually within the security model. for PS.