Word doesn't do magic, but it does provide all the tools you need.

As Charles indicated, what you should be doing is using a separate template for each company with the Styles in a given template formatted accoring to that company's requirements. That way, when you create a new document for company ABC, using the ABC letter template, all the required Styles will be there, with the required page layout and paragraph formatting. Use the ABC memo template and the page layout and paragraph formatting for an ABC company memo will be there. For company XYZ, you'd use equivalent templates specific to that company.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]