This is a classic case of a user trying to design a solution themselves, rather than just stating what problem they are trying to solve.
Ask the user what they want to achieve with this interaction.
Once you have this information you are in a better place to discuss alternate solutions.
(Asking questions is a good strategy to get someone to be open minded. Telling someone they are wrong will just make them defensive and more likely to stick with their original position.)
I strongly suspect that they want a mechanism to be able to easily find the items they have just changed.
A better solution for identifying changes would be to highlight the rows with changes in a different colour. If you have a large volume of rows (i.e. you have rows that are off the screen), you can also provide a filter that will switch the view to show only the rows with changes.