Hi @highfresh 

Yes, you can add a banner in the New ticket page in customer portal via portal customization. To do this, please navigate to  Admin>Support Channels>Portals>Customize Portal>Layout & Pages>Portal layout>New Ticket and you can insert the below script-

<script>
jQuery(document).ready(function(){

jQuery('.new_ticket_page .heading').html('Submit a ticket<div class="information_text">If you have already raised a request in the past 48 working hours, please do not raise another request</div>') 

});
</script>

Expected Outcome- 

Now this will insert the text with the same font styles as Submit a ticket but if you note the code we have defined a separate class for the text. We can include styles for the class on the Stylesheets page, like,

.information_text {
    font-size: 14px;
    font-weight: normal;
    color: #3333c3;
}

Notes : i. We need to work with both CSS and JS to achieve this, the CSS part is optional but will be useful to style the text, else it will take the default styles,

ii. Since we are inserting HTML using the function, it is possible to include a hyperlink as well in the banner. For instance, .html('Submit a ticket<div class="information_text">If you have already raised a request in the past 48 working hours, please do not raise another request. You can check your previous ticket <a href="htpps://support.freshdesk.com/tickets">here</a></div>') will add a clickable link to the text which can redirect users to another page.

iii. In the code, .html('Submit a ticket<span class="information_text">If you have already raised a request in the past 48 working hours, please do not raise another request</span>') - Changing Submit a ticket or removing it will remove/change it from the new tickets page too, only modify what is inside "information_text" but if you want to change the Submit a ticket test, feel free to do it. 

Cheers

Barun