I’ve changed the post title to reflect this, thank you.
At the moment, I don’t believe we have plans to implement this, as this will cause conflicts with content found in user’s local versions of the note in certain instances.
You can however add a new field to a existing note type: How to add a new field to a note type from a deck on AnkiHub
In your case, you could delete the notes you want to switch to clozes, then add the new cloze note type and suggest them. But I know that wouldn’t be ideal and would cause scheduling loss