Properties in 2,8 can be overridden per Collection. The way users add a Collection Override, is by right-clicking on a property and selecting Override. This then shows a list of Collections which this object exists in. Most likely there will only be one, but Blender 2.8 does support having objects in multiple collections, so you may see more. The user select which Collection he/she wishes to add the override to.
This adds and entry to the Collection Properties. Here you see a list of properties which the Collection is overriding. From here, you can adjust the overriding value, or remove the Collection Override.
When linking in data from other files, users can selectively override linked properties.
to get started, users must navigate to the relevant Properties area. Because the Datablock is linked, users are not able to change any values.
To override a value, the user clicks the Override icon at the top to set the current data block as overridable. Then, to override a specific property, the user then changes any value below. Any values that are overriding turn teal. The rest of the properties still get their values from the linked file.
Properties Override Visual Design
In Blender 2.8, properties can have one of eight states, as illustrated here:
This is getting to be quite many, and just relying on colors is starting to become slightly unclear.
We want to make this more clear, by using tooltips to tell user which state the property is in, and, more importantly, why:
This document reflects the current state of the Override UI design