David,
Currently, this is not very easy to do (and there is rarely any need to do it). Perhaps you can share some more specific details about the particular challenge you are trying to solve. Why do you need the extension to fire after the tag?
Thanks,
Craig.
Check out our new Swift integration library for iOS, macOS, tvOS and watchOS: https://github.com/Tealium/tealium-swift with updated documentation https://community.tealiumiq.com/t5/Swift/tkb-p/swift.