How to prevent Drupal export XML formatter adding paragraphs?
I don't think there is a need to make a "special module". Instead you could install the Forena module (with quite a few official D7 releases ...), as an alternative to what you're trying to do with the Views Data Export module (or the Views Datasource module as suggested in one of the comments to the question here).

You could use the Forena module to create an appropriate report. As per your comment like "Full nodes, no. Only some choosen fields, but all of a single content type." such report should be straight forward to create. And then create an XML file from the report data (= query results). Similar solution for somebody who rather wants/needs a JSON format. Refer to my answer to "How to add a link to the CSV download to my module page, for a report created with Forena?" for more details about all sorts of export formats, and some online demo samples.

Using this alternative, you probably don't need your (not ideal) work-around anymore which is to disable changing new lines to HTML new lines.