Yes, you can add a recipient's email to an existing campaign.
To add the email:
- Go to Partner Center > Businesses > Accounts.
- Find the account associated with the email, then click on the account name. This will bring you to the account details page.
- On the account details page, scroll down to the Users section. Click the menu icon beside the User you want to add to the campaign.
- Select Campaigns from the menu.
- Find the campaign you want to send to the User, then click Start next to the campaign name.