If you use Microsoft Word, you may be interested in a free ebook by Rondina Muncy: Automatically Numbering Your Genealogy in Microsoft® Word. It tells the reader how to renumber genealogies using both the Register (created in 1870 for use in the New England Historic and Genealogical Register published by the New England Historic Genealogical Society) and NGSQ (National Genealogical Society Quarterly) styles without manually going back and correcting their numbers.
The 27-page booklet is full of screenshots that illustrate the methods described. The methods described work in Microsoft Word on Macintosh and Windows.
Automatically Numbering Your Genealogy in Microsoft Word can be found at AncestralAnalysis.com. It is the first item under “Articles” and can be downloaded.