I have a very complicated project, in which i have to handle almost 30 different (final) styles.
And to do so i have to “simulate” the styles in SN too, because it’s impossible to change all the styles later in the word processor (Word or Nisus).
My question is: is there a way to export to XML?
Exporting to Flat XML is the same thing?
Adobe Indesign and other similar sw can read Flat XML?
Or XML would be better? If yes, no possibility to do it?
The MultiMarkdown workflow does support Flat XML output, complete with stylesheets, but that requires adopting what amounts to a plain-text writing environment, which is not everyone’s cup of tea. It’s basically just Markdown with some extra syntax useful to authors, such as footnotes, cross-references and tables. Furthermore, that workflow isn’t really tailored toward arbitrary stylesheet design. It can be done, but it requires developing scripts (probably using the XSL post-processing system) to get your custom syntax turned into styles—it’s not something I have ever looked too deeply into. I’ve developed custom XSL for LaTeX output which essentially accomplishes the same thing, so I know in theory it is possible.
Otherwise, sticking with traditional formatting, you can get a stylesheet applied to a consistently formatted document with Word, without too much hassle. So long as each range of text that will be associated with one of the thirty styles is unique from all the others, you can use Word’s select similar formatting tool to select all text in batches, and apply the style to that selection with a single click. It’s not something you’d want to do on a regular basis with that many styles, but it may be an improvement to whatever you’re doing now.
Yes, actually i do in this way you just said, but i can’t find a way to apply (in Word) different styles to word (that are written in SN with different styles) if the words are in the same line…
it’s impossible (for me)… 
So I thought: I know SN is not intended and thought for people who need to use a lot of styles, but it’d be awesome to have:
Last question: is it maybe possible to manage with words different styles inside the same line?
Maybe it’s just my fault.
Forgive me if I speak out of ignorance (not knowing what SN stands for) but if this is about a Scrivener project, and if you are finalizing the document in Scrivener and using the other word processing programs only for the lightest of final touchups, or submisstion, you might try the following:
now this method won’t (?) include document titles or folder titles unless I am wrong (quite possibly there is a scrivenings setting to make them appear), so you would need to include these titles inside your documents. And this will at most preserve font and presentation style information only; every paragraph in ms-word will almost surely list itself as “Normal” or “Default” but at least you should get a document that looks just the way you want it.
I did not have a problem doing that with MS Word 2010. Say I have a paragraph of normal text, and within that paragraph there are two bold words that are blue. I duplicate that formatting elsewhere in the document. Then I right click on one of the blue words and choose the Styles/Select Text with Similar Formatting contextual menu command. All of the bold blue words in the document are selected, and I can apply a style to them without impacting the other text on the lines they fall within. Is this the tool you are using? Maybe it does not work so well with the Mac version of Word.