The vutil -unload and -load options will produce much faster results in moving the data from the old file to the new file.
First, unload the data into a binary sequential file using:
vutil -unload -b originalfile tempfile
Next create the new empty file with an OPEN OUTPUT from a COBOL program.
Next, after you have an empty file with the new definition load the data with:
vutil -load -b temptfile newfile
Lastly rename the newfile with the original file name.