As my understanding you are trying to disable USB blocking feature to selected computer. ? for this you have to create different agent configuration file which is not contain USB block and then apply this agent configuration file to the selected pc from policy cataloge.
I don't want to disable USB blocking for a computer.
I want to allow a computer to use a storage device with a specific S/N.
I have to policy configured right now to allow a storage device that matches a certain S/N. That works.
However, I want that storage device only to be used on one computer.
As the policy stands now, since the S/N is allowed, it can be plugged into any machine on the domain and be used.
I want to limit that use to one machine.
I understand you required exception on computer based , Create 1st policy to block every USB device and applied to all computer , then create another policy which exclude the S/N and apply this policy on specific computer from ePO policy manager