Hi @Nagashree Balasundaram Thanks for reaching out. As mentioned above editing the content as part of HTML is possible for the inbuilt template but you will not be able to add a new template under the notifications template blade.
as the content is in HTML you will be able to add a Logo, email signature, disclaimer etc. to the message content.
example for adding a logo: <img src="https://google.com/mylogo.png" />
Do let me know if you have any queries. I would be happy to assist you.