It is absolutely possible to have follow-up emails sent in the same thread as the initial email.
If the subject line of the follow-up email is left empty, the follow-up will automatically be attached to the same thread as the initial email and will re-use the initial email's subject line.
Keep in mind that to ensure emails are viewed as conversations in the recipients' inboxes, recipients should enable this option with their email provider.
These Outlook and Gmail articles explain how to toggle this setting to enable group conversations within a mailbox.
💡 Please note that as this option is set at the inbox level, it cannot be set within Hunter.