Thank you for your answer.
It's very unfortunate, that itch.io doesn't have this feature. I'm quite positive, that most developers would benefit from it (A pre- and post donation message, that is), but well...
And I too like to think of donations as real donations, but I'm pretty sure, that there will always be people expecting you to churn out more content in less time and the last thing, I want to do, is give people the wrong impression.
So I have one last question, since you have a mod tag:
Can you move this thread to the ideas and feedbacks-section please?
Or would you recommend me to make a new thread?
I wholeheartedly believe, that every developer would like this feature.
Thank you again for your answer.