What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Can you please be more specific in your request? Only customization that you can do inside of custom URL related to username is to add name to URL. If you want to find out more about this you can read following article: http://www.jotform.com/help/261-How-to-create-a-Custom-URL-of-a-form
In case that you want to achieve something else, please can you explain what you want to achieve and we will be happy to assist you.