You should be able to target your relay selection policies to any grouping of machines, based on virtually any criteria. When you multiple-select several computers, and right-click --> edit computers settings, you are presented with a dialog with 4 tabs. The first tab will let you input your setting (relay selection is controlled via a setting), the second tab allows you to target to a group of machines. On the second tab, you will want to chose the second radio button to target all machines matching your subnets. The third tab is more messaging (you don’t want one), and the last is for constraints. You should uncheck the ‘ends on’ box to make this a policy.
You can also setup a more complicated policy with custom relevance. See the following post for examples on how to do dynamic bandwidth throttling. The steps are the same, except you want to set the __RelaySelect_Automatic , __RelayServer1 , and __RelayServer2 settings.
Finally, we do have a hierarchy for settings actions. The most recent one will always take precedence.
I hope I’m steering you in the right direction. If not, please expand a little further on the details of the relay selection policy you’d like to put in place.