That is not an obligation. Manufacturers are allowed to improve their vehicles without doing retrofits on the entire fleet, and Tesla is no exception. Their obligations are to keep the screen functional (and obviously to get rid of the yellow bands for aesthetic reasons to improve customer satisfaction.)
Some people report that the screen's functionality is impaired, so Tesla must do something, but you're not entitled to decide what they do.
They have an obligation to make sure the MCU display is physically clear with no yellow border.
If someone has trouble reading the screen because of the yellow border, then the functionality is indeed impaired.
And even if something is only aesthetic, it should still be fixed under warranty. What if white seats start yellowing out in certain areas after barely a few months of use. Any reasonable person would consider that a defect to be fixed under warranty.