Can I use a generic region code like "EU" for Europe?

Not at this stage.  It's not possible to enter a code like "EU".  You need to enter all individual country codes, for where you want the redirect to be active.

For example, if you want people in France, Germany and the UK to see the redirect, add "FR, DE, GB" into the settings.

For a list of country codes and a screenshot of how to do this, see this thread: https://shopifyninjas.zendesk.com/entries/53547574-Do-you-have-a-list-of-all-the-country-codes-