The counting macro will allow Google Ad Manager (GAM, DFP) to count clicks together with the third-party ad server.
If this counting macro is not inserted within the third party tag, the click will only be registered in the third-party ad server, without being counted in Google Ad Manager.
Almost all tags support third-party click macros, some may require an additional URL parameter (e.g. &click=). If you receive a tag that doesn’t support third-party macros or if its not listed here, you should request assistance from the advertiser / agency / network who sent you the tag.
Changes to the tag can be performed by anyone.