importing customers without passwords

Hello,

I have been running ProductCart on our site for about six months.  While redesigning the site last summer, we decided to let customers create their own accounts as needed on the new site design (i.e. we did not import any customers from our old database... though it did exist, there were no web-accessible customer accounts available on the old site).

Now we want to import a select group of customers from the old db so that they can be assigned access to a private sale.  If we use the customer import tool, I see there's a field for password.  We thought we would leave it blank for all those who haven't created an account on the new site in the last six months.  But of this group we want to import, some customers *have* created an account in six months.  Would I overwrite their password if I import?

I expect to import as "updating" fields rather than adding new.  But if I import their email address and leave password blank, the PC wiki tells me it will generate a new random password.

Maybe I should import as "add new" customers?  Then would it see any already-existing customers' emails that are in the list, and reject the one I am trying to add?  That would work if that's how the import tool functions. 

Thanks for any help in advance.  I'm a bit bleary-eyed at this point...!

Thanks Hamish.  This is indeed what I did to solve the problem!