It is possible to edit the picture (thumbnail), headline, and description, but only for URL links that have a verified domain on Facebook.
"The integrity of content on Facebook is a serious concern, and domain verification is a step towards ensuring that only verified owners can edit the way their content appears on Facebook. Many publishing apps use link editing to customize and create engaging content for the Facebook community. In an effort to preserve this essential functionality in a way that protects the integrity of publishers' content, verified link owners will now have the ability to overwrite link metadata when creating link page posts. Source
So, you have to add your domain to Facebook Business Manager. But don't worry 🙂
Here are some links for Facebook articles with steps on how to get the verified domain:
How to Verify a Domain
💡 Please note, the supported ratio for the Link post thumbnail is 1.9:1., If you upload a picture with a different ratio, Facebook will crop the picture to the required 1.9.:1 ratio.
You can find the premade size for Link post in our Image Editor, where you can double-check the size. 😉
When creating a link post, after you paste the link, you can edit the title of the link you are sharing and upload a different image to the preview (thumbnail).
to change the title – click in the area of the title, and it will turn yellow; this indicates you are in the editing mode
to change the thumbnail – click on the Upload button and select the image from your computer
If you have any questions, don't hesitate to contact us via the in-app chat.