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This plugin adds a simple post-type drop-down to the post editor interface, allowing you to reassign any post to a new post type. It allows you to switch post’s type while editing your post.
The plugin can convert nearly every combination of posts, pages, and even custom post types:
As of 3.0.0, support for switching to or from Attachments was removed. This may come back in a subsequent version.
Invisible post types, such as revisions, menus, etc., are purposely excluded. But, if you need to access invisible post types, you can adjust the boundaries using the ‘pts_post_type_filter’ filter.
With bulk editing (thanks to Matthew Gerring) you can select all the posts in a certain type and convert them to a new type with one quick action.
With block-editor (aka Gutenberg) support (thanks to Daniel Bachhuber) you can switch between post-types that use either the Block Editor and the Classic one, without losing any of your embedded content.