OK. But this was the one mechanism out of Kirk’s control or reach. He had no way to manipulate or control the Guardian. Spock did not have access to the Guardian, etc. As soon as Edith died, they jumped through the portal. That was the Guardian, not Kirk and crew. They were at the behest of the Guardian and they chose that.
That being said, there is nothing stopping Kirk from breaking Time Travel Prime Directives that haven’t been invented yet and grabbing the Guardian by its…whutever…and robbing Edith from the past.