To unblock a device you have to scroll down and manually search for the device. There is no search feature to make this easier.
You have to create a group for each USB device you want to exempt for devices. For example, I have all my computer in one group to have USB devices as read only. A user requested to have one specific type of USB as both read and write. I can't just find the computer within the existing policy and exempt that USB for that particular machine. Instead, I have to create a whole new policy. We have a very decentralized environment so if 100 users need 100 different USB's unblocked from each endpoint we have to create a 100 different policies.
John Veldhuis commented
2. Why not use a user policy?