Hey Steve,
I am really sorry for the delay of this reply as it is a weekend for us here. I am sorry but unfortunately there is no way to do that right now
The new composer that we introduced in EasyBlog 5 is very sophisticated in it's way where it actually stores a lot of rich data when you are composing blog posts. Most of these "rich" data is being added while you are composing the blog post without you knowing at all.
For instance, when you insert a "link block" into the composer, it actually stores the url, response, open in a new tab, description of the url in a json string which is then sent back to the server when you save your blog post.
In order for the new composer to be able to convert your blog post format into the composer format, there are over thousands of operation that needs to be done, let alone the script needs to scan through every single "html" tags in the content to determine it's block type and unfortunately the accuracy is probably going to only be 20% - 30%
I certainly do hope that this would be possible as it makes all our operation so much easier though.