Thanks for the screenshot.
Please understand that such in-depth customization help is not provided, per our Scope of Support / Terms.
From time-to-time, we are able to go a bit above-and-beyond to help out, and I’ll see what I can do for you.
If you need some coding help–now or in the future–you may want to ask your developer or reference our documentation and list of known customizers.
For your customization request, please confirm that you want a specific piece of text to be inserted by default whenever creating a new ticket (pre-fill the ticket’s Description) but if modified, use the modified version. Correct?