I have found the answer to this:
viewtopic.php?f=4&t=1483 (YubiKey Personalization Tool > Settings > Output Format, then Update Settings button > select configuration slot 1 or 2 (you will need to do this process twice if you need to change the Output Format for both slots), and then click on the Update button.
When you first change the Output Format you will see a message to the effect that the settings have been changed, but ignore this, because they will not have been until you click on the Update button on the Update Settings tab. - Be careful using other settings, like Configuration Protection, on these tabs, too, because they will almost invariably screw your configurations up quite badly (not because they do not work, but because several of them do not play nice with the other features on the key - you will either find that settings on the Settings or Update Settings tabs will over-ride everything (including settings on the other configuration slot), or will conflict with settings when you try to set, for example, a static password (which has its own Configuration Protection that should always be used to protect a static password slot in place of the Configuration Protection on the Update Settings tab.