Can you add a new section into an individual email without creating an email template?

Yes, go into the HTML of the email. I advise to clone the email and make design changes on the clone. Copy the HTML code of the section and paste right below. 

You will need to know how to read HTML. Not sure how you're templates are coded, it all depends on the structure used to ensure proper responsiveness etc. 

This can be done while editing the draft by going to Email Actions > HTML Tools > Replace HTML.

Thanks Tim & Grant. I tried this and got a response saying I cannot replace HTML if using dynamic content (which is why I want to have a second section).

Let me take a step backward. I am trying to create 1 email for 4 different senders with dynamic content within the email. So if a Sales Rep = Jenny then from name = Jenny Lastname, email = Jenny@mycompany.com. and signature block (the second section I am trying to create) = Jenny Lastname & contact information.

Make sense? Thanks!

So it's a combination of both Grant's and I's suggestion. You need to go into where he said and take your paragraph section where you see mktEditable. Make sure you copy the appropriate length of code as it can cause issues with design.

This bit of code will also have an ID assocaited to it that defines your editable content. This is important for grabbing snippits dynamic content.

Hopefully you grabbed the right code and you can now see a new section. I'd label the ID someting other than what you have now. 

Are you using segments for your 4 senders? Snippits for your signature block?