Trust me, you don't want to do that. The same layout is really not recommended because it will generate extra html inside the editor that will pollute the message and will make it difficult to edit. I might be possible to show a basic quote layout using the q html tag (or blockquote but since it's already used as the message parent tag, I'm not sure) inside the editor that will be transformed to the quote bbcode after, but as you can see the quote element of XenForo has some information: the author & the source. So this will require a js interface to edit quotes (to access the author and the source data) which is not convenient. So we're not here with just a basic quote as it can be done with a html tag (you can check here and press the quote button to see how it is managed in wysiwyg).
But to answer to your question, you will have to modify the XenForo Wysiwyg & BbCode Formatters, then synchronise them together.