You can edit the agent locations for multiple devices at once on the Device Manager screen.
Here is a video tutorial to add a new location to multiple devices.
First select the check boxes next to the devices you wish to update.
Next, click on the Action menu in the header of the platform you wish to edit, and click the Agent option.
This will bring you to the Agent Location Selection page where it shows the locations across the top, and the selected devices across the bottom. From here you can select locations and chose to either add or remove selected locations from the selected devices.