See
http://word.mvps.org/FAQs/Formatting/WholeDocumentReformatted.htm
as to how this is possible, the article is actually the opposite to what you
want, but will be of interest.
Most users find this setting more of a problem than a requirement.
There are other ways of reformatting a document quickly BUT all rely on the
good use of Styles. If the document does not have Styles used properly, you
will have to go through the document manually.
There are tricks of applying styles rapidly through out a document, this
include the use of Find/Replace, F4 (repeat), etc.
Once a document is setup with good styles then you can use Find Replace to
change applied Styles quickly, this does not change the Style Settings but
applies manula formatting.
If you want to change the Style, the Styles and Formatting Pane can be used
to modify the Style but wont necessarily change all occurances in the
document.
In the pane there is an option for the specific Style to select all
occurances and apply the modification. This could be grayed out, this can be
turned on under Tools, Options, Edit tab, check Keep Track of Formatting. I
personally have this option turned off as it activates other features that I
don't wont to see.
Without this option activated you can still use the Styles and Format pane
to document-wide reformat a Style.
Go to text with the style you wish to modify, manually change this with the
attributes you want, open Styles and Formatting Pane, scroll to the style,
clcik on the down-arrow and click Update to Match Selection, this will change
all occurrances in the document.
This sounds alot but actually works very fast and good results can be had.
Hope this give you some help.
DeanH
