(This blog was written for versions of OpenOffice up to Version 3.4.0)
If you change margin settings on a lot of documents used, it is possible to set these margins as your default (Opening that way each time)
To do this, you need to create a new template with your preferred margins.
1. Open a new document of the appropriate type eg Writer or Calc etc.
2. Go to Format > Page... > Page, and adjust the margins as desired > Click OK.
3. Go to File > Templates > Save..., and in the Templates window - give your new template a recognizable name, and click OK to save it.
4. With the document still open - Go to File > Templates > Organize...and in the left hand side of the Template Management window double click > My Templates > Click the name of the template just saved and then click Commands drop down arrow and from the list click > Set As Default Template.
In future, when you create a new document it will have the margins you have chosen.
If for some reason you wish to not use the default page settings for a particular document it it possible to change the margins for that particular document by > Format > Page and from the Page Style: Default window click on the Page tab and in there alter the margins as required for the document being done and click OK.