Application library items can be found in Library > Applications. Built-in application library items can be found in Library > Applications > Built-in. You can view built-in applications, but not edit. You can define custom applications in the library or for each appliance group in the optimizer tree of the desired configured appliance group.
You can edit built-in application in the appliance but EMC will not allow you to import that application in the library stating application already exist in the library with same name.