Which command has the same effect as clicking the update button in the GUI?

Clicking "Update" in the TMUI results in modifying a configuration.

Instead a "Finished" results typically in creating a new configuration object.

It is comparable to a PUT/PATCH (modification) versus a POST (creation) via the API.

In TMSH (command line) you may want to use the modify command:

tmsh::modify 

To create a new configuration object you would use the create command in TMSH instead:

tmsh::create 

Be aware, that changes through TMUI apply to the running config and will also be saved to the startup config.

Changes through the API and TMSH are applied to the running config only. They are not automatically saved to the startup config and might get lost with a service restart. Use the save command, to write changes to the startup config:

tmsh::save