The list of available templates you see in the template drop down list will be relevant to the record type you are in, or the submissions workflow state. For example, if you are on a contact record you see email templates relevant for contacts, whereas if you are choosing to send an email from the interview tab of the submissions area you will see interview email templates.
Once the template is loaded you can treat the email as per any normal email, for example, editing, attaching documents, executing merges etc.
If the wrong email template was selected, you can simply choose another from the list, or use the Clear Email option.
