the MFS splitting function (from the MFJ file) is one of the cool things available in Lacerte.

You mentioned  "The MFJ vs. MFS Comparison".   Were you referring to  the MFJ/MFS Wksht?

(1)  If yes, that would mean you check the MFJ vs MFS Comparison box in the Filing Status Section of Screen 1 (Client Info).  If so, in the MFJ/MFS Wksht, do you see the Greenish link (CLICK HERE TO SPLIT THIS RETURN)  below the line of 

MARRIED FILING SEPARATE GENERATED A TENTATIVE TAX SAVINGS OF $XXXX?

Click the greenish link and the MFJ file will be split into two.  NO need to retype the info.  The MFJ file remains intact.  Of course you would need to make the necessary changes in the TWO MFS files.

(2) If NO, go to Screen 1, and check the MFJ vs MFS Comparison box in the Filing Status section.