Yes. An old post can be a great source of inspiration. You can pick out interesting concepts, settings, or emotions from it. Then, use your creativity to weave them into a new and unique story. For example, if the old post mentioned a lonely forest, you could write a story about a character who gets lost in that forest and their adventures there.
Sure. You can take the essence of the old post and run with it. For instance, if the post was about a strange object, you can create a story around the origin of the object, who it belongs to, and why it's so strange. You can build a whole world around this object, introducing characters who are either intrigued by it or afraid of it.
Of course. The old post can act as a springboard for your creativity. You can adapt and transform the ideas in it. Maybe the post was about a particular time of day, like sunset. You could then write a story that revolves around the significance of that sunset for different characters, their hopes, and dreams associated with it.