I had these 2 links concerning re-factoring in my archive
http://labviewguy.com/refactoring/
http://www.ieee.li/pdf/viewgraphs/refactoring_labview_code.pdf
They help break it down into parts to think through but I've not found any silver bullet when it comes to re-factoring.
I always seem to have lots of backups and forced to do lots of testing. Commiting often to Source code control was a big help in my last re-factoring project.
Mark