You can define the default system security settings on the system-level Security tab. (Click Default in the Projects tab, or click Security in the Users tab of the CS-RCS Properties).
For all projects where the 'Inherit permissions from system' option is set, permissions are inherited form the closest master project, up to the system default. You don't need to redefine the security groups, as permissions set at higher levels are accumulated.
Tip: Click Report on the project Security tab to see all permissions inherited by the project.