Custom Templates for Comment Externally vs Internally

By default now, when an Agent goes to Add a Comment, the text box is filled with:
Hi [firstname] [lastname],
– [Agent Full Name]

There are two requests I'd like here:
1. I want to be able to change the template for this.
2. I have to delete all this information, and then enter in my desired comment if I want to comment internally. I'd like to select which type of Comment this is, Customer (use template) or Internal (don't use template), and then hit OK to submit the comment.