Add comment by change drop-down list

[Edition Nehemia]

Hello all,

I would like a comment to be displayed automatically when the status is changed. Because this is an important step. I have saved the status in a drop-down list.

How can I do this? Is there a way to do this with an automated action, e.g. with PHP code?

Or in other words, which PHP class do I need to call in order to create a comment properly?

Kind regards
Christoph