I have a requirement in which when the vision client is updated, my client tag should be updated with a value of 1.
Please let me know if you have any ideas to fulfill the requirement of executing a script only when the Ignition vision client is updated.
There's nothing that will do that. However, if you set project update mode to None, you can use scripting to perform a client update as described for system.vision.updateProject(). Such a script would be able to perform whatever other special actions you want.
ProjectUpdateAvailable tag could be watched to know when an update is pending, but unless you script the actual update as Phil mentioned, you won't know when the update actually happened.