Use a message template from admin panel

Is there any way I can use a message template from the admin panel?  What I'd like to do is trigger an email to a customer from the admin panel.  I have a custom email template (for repetitive emails - becoming an authorized dealer - which includes and attachment), but no way to trigger it.  Any help would be awesome!

You can see message template list here.  You can chnge any of the template. If you want to add message template and send it according to your requirement, then you have to use plugin or change core code.