Turn Off Revision Marks for Formatting
The Problem:
Format changes are always tracked if tracking is on. Sometimes it's useful to track them, but in the kind of work I do, it's usually not. Is there any way to make tracking these changes optional instead of inevitable?
The Solution:
No, but you can at least hide the marks for formatting changes. Choose Tools 
Options, click the Track Changes tab, and select None from the Formatting drop-down list (or, in Word 2000, the "Changed formatting" drop-down list).