Paul,
If your gedcom file is in 5.5 format, there is a way to update all these tags in one go using the format conversion to 5.5.1.
Save your gedcom file before doing this.
Make sure your gedcom file is in 5.5 format (either "No" will be shown in the screen below, or you can directly look at the header section of the text file : GEDC 2 VERS 5.5).
Then go to File/Properties.
On the following screen, choose "Yes" for the 5.5.1 norm and continue until the other screens. Finally, click the "Finish" button to run the modifications.
Il should do the job.
Let me know.
Frederic