No. There is no such setting.
You could use a macro that would do this for all documents in a particular folder.
Here are some pages that could get you started with this:

• http://word.mvps.org/FAQs/MacrosVBA/BatchFR.htm - find and replace
• Batch process Word documents - Graham Mayor

Graham has a number of batch operation Add-Ins but I think the one shown above would work for you. You will need to create a macro for the conversion to A4. His Add-In page has instructions on what is needed for the macro. It will then run it on all documents in a particular folder and its subfolders.

Be sure to change the normal.dotm template to A4 size.
Normal Template in Microsoft Word - How to Find or Open the Normal Template

When you say precedents, are you talking about Templates?