Hi Nathan,
You can still send email communication when your event is closed. Are you sure you were clicking the "Resend Confirmation Email" button and receiving multiple results?
You can send custom emails by either going into the email itself in Promotion & Communication > Email > Event Emails > Click on the email > Send > Manually > Check off everyone > Send; or you can do it through Invitee Management > Manage > Invitees & Registrants > Check off who you want to send it to > Bulk Actions > Send Email. Click "Using an email from this event," and you should be able to select a custom email to send.
Keep in mind that emails sent the second way, through Invitee Management, do not pull into any of our email tracking reports. So if you'd like to be able to report on whether the email was opened or not, we advise that you send it through Promotion & Communication instead.
Best,
Julia