Hey Paul!
Domain and User Propagation sounds like what you're looking for. One thing to keep in mind regarding throttling: both users AND domains can be throttled separately. So you would want to propagate the user's throttling settings, rather than the domain's.
To propagate the user throttling setting, log in as the System Admin and click the Settings icon. Expand the Defaults folder and click on User Defaults in the navigation pane. On the Throttling tab, change the threshold and action to whatever you'd like all users to default to. Once those settings are saved, click on User Propagation in the nav pane. On the Options tab, choose whose settings should be changed: All Domains / Specific Domain or All Users / New Users. Then go to the Throttling tab, select the settings that should be changed, and choose Propagate Now in the content pane toolbar.
Using Domain Defaults works similarly: configure the settings domains should default to, then propagate the ones that should be changed right away. I've listed some articles below that should give you some more info. If you have any other quesitons, feel free to ask!
Thanks,