🚀 go-pugleaf

Manually is one way that comes to mind: 

1) Create the new format. 

2) Perform a Find "Cross Reference of Format:" (make sure you supply the format name). 

3) Double-click each x-ref as it is found and manually replace the old format with the new one. 

4) Search for the next instance of the x-ref. 

Otherwise, if only the format definition changed, but the x-ref *name* remains the same: 

1) Change the definition in one chapter and save your changes. 

2) Open your book and select the chapters in which you want to change the x-ref definitions. 

3) Use File > Import > Formats to import into all the chapters of your book *only* the x-ref formats from the one chapter you modified. 

Or, maybe you can search and replace the MIF files. See page 48-ish of the MIF Reference Online Manual, which is in your Online Manuals folder in your FrameMaker installation path, for info on this. 

Cheers, 

Sean