This has been implemented in SC 2.3.22 (this was funded by 2 SC Premium license holders that wish to remain private)
As per title, I've added a "Convert post to update" function for Showcase.
This is a Forum Moderator function which requires the Forum Moderator permission "Showcase: Convert post to update"
When viewing a thread that is of the Thread Type 'sc_item' (a thread that is associated with a Showcase Item) and the viewing user is a moderator and the viewing user has the above moderator permission, then they will see a link "Convert to update" (as shown below).
Note: All of the content boxed in RED will be converted (Post Text, Post Attachments and Post Reactions).
Clicking on the "Convert to update" link will launch an overlay (as shown below)
Simply set an Update Title (as shown below) and click on Confirm button
And here is the result... a new update added to the Showcase Item.
As you can see, the update title is what you set in the convert to update form, the text from the post is the text for the update, the attachments uploaded to the post have been converted to attachments uploaded to the update and the reactions for the post have been converted to reactions for the update.
And if we go back to the thread and look at the post, the text has been replaced with the same text as if the updated was posted to the item and auto posting in the thread was set (same phrase, same data passed into the phrase). The attachments are gone and so are the reactions.