How to change customer group of unregistered customer

Hi,

Customers who decide to checkout on my website without registering are assigned 'Default' as their customer group. I would like to change some of their customer groups to a different one. However, when I look up the customer by name, I obviously can not find them as they are not registered. However, I would still like to be able to change their customer group, because when I look up their order, it shows that they are assigned "Default" as customer group.

Thank you.

Version?

Not doable.

1.5.5.1

I suppose you could play with Guest as a Customer Group, and with Search (button top right) for that.