In case of inheritance I have checked that we are not able to assign permission level without STOP inherit from parent website. I have observed that you can assign permission level at newly created security group at site level but the fact in this case is SharePoint will ask to STOP inherit permission and convert it into "Unique Permission" level.So in bottom line if we create new groups e.g. Americas Operations Demosite Administrator with option "Use same permission as parent site" as SharePoint current Security model will not allow you to assign permission level without breaking inheritance that you can see in below screen. That means in case of ANY SITE CREATION if we create our own groups then it will be worthless without permission e.g. Americas Operations DemoSite Administrator.
Posted by Vaibhav Jain (Success is always one step ahead)