getDare allows users to update their posts up to 103 hours (4 days, 7 hours and 25 minutes). There are several alternatives.
- Post an image with a direct permanent link (
read this blog) that you can update.
- Post a link to a document elsewhere that you update (as you said yourself).
- Posting many permanent shortcut links in the first post that you can update later on so each of them can be redirected to a later post of yours.