If I provide an #AltText for you, it's 100% OK to edit your post to put the text in. And if you do, I will happily delete my reply. I'm not looking for credit; it's fine if you and I collaborate to make it look like your image had an alt text all the time. In fact, that's what I want! That's the best place for the text, not in a reply where people have to go hunting for it.
So if you reply to my alt text with thanks, be ready to delete your own thanks after I delete my post. 😉