How can I preserve the text appearance when I replace the selected text using HTML or Markdown?

[jhonattan-inner]

How can I preserve the text appearance when I replace the selected text using HTML or Markdown doing a merge?

I tried three different approaches, but I could not preserve the same selected structure.

Flow the link with the example:
https://codesandbox.io/p/devbox/kind-oskar-yn7c4y?file=%2Fapp%2FEditor.tsx&embed=1

Will be good if has a way to change the selected text between different blocks doing a merge with these blocks and the new content, by Markdown or HTML.