I can not find anywhere in Mojo admin to control the text of the standard emails that go out.  I can't image you need to customize mojo to do this.  I saw something about custom event handlers, so maybe that is the option for advanced users/developers, but it is still hard for me to believe there isn't something a normal site admin couldn't use to manage email templates in the core and in the subscription pro module.

We are looking to do the following with an HTML editor type of feel ... or at least have a portion of a standard email have an area for customization to:
1) Send custom text and description of the value of membership when someone joins/registers for the website (editing the welcome email). 

2) Send an email with custom text after a purchase of membership subscription.  I see the reminder email templates, but how do we send or control the content on emails that go out on the original purchase or renewal?