Provide the ability to create one or more Security templates.
Creating a new template would basically contain everything you would normally see under the Security tab. You adjust your settings and give the template a name. You should be able to create multiple templates.
Then, under the Security tab for a site you would see what you normally see to allow you to adjust settings for that one site, but you would also have the option to pick and apply one of your templates.
Choosing a template basically applies the template's settings to that site in one click.
The other part to this would be that if you subsequently edit a template and save it, it should apply those changes to all the sites currently using that template (maybe a pop-up listing all the sites about to be affected would be helpful so you can cancel still).
The final bit would be that if you go to a site's Security tab, and that site is using a template, if you make any individual tweaks to the security settings then the system should (with a warning) decouple that site from the template, i.e. that site is no longer using a template (to allow for ad-hoc site security), and likewise, changes to templates will no longer affect that site until a new template is chosen for that site (if that's what's decided).