Reload form and update dropdown list after modal entry

I have a form with a dropdown that a user selects to categorize the form entry. There are times that the user will need to add additional categories to the list if they are not present. It would be helpful if the user could open a modal window to the category form to add another category to the list. Once they submit the entry in the modal form the dropdown list will refresh. I am not sure how this affects the parent form if the user has already entered data in the parent form.  I am not sure if the dropdown list can update without affecting the parent form's entry. Possible fix, save parent form as a draft while refreshing dropdown list.

I did find a forum post with another user explaining a similar situation. They did post some code, but I am not sure if it is the entire code to solve this problem or where to even place the code. Here is the code below.

function getAjaxVariable(variable){var query = variable;var vars = query.split("&");for (var i=0;i<vars.length;i++) {var pair = vars[i].split("=");if(pair[0] == "value"){return pair[1];}}return(false);}jQuery(document).ready(function($){$( document ).ajaxComplete(function( event,request, settings ) {var query = settings.data;if(query != undefined) {var res=getAjaxVariable(query);if(res=="Deposit+Paid" || res=="Enquiry" || res=="Booked" || res=="Balance+Paid" || res=="Pending" || res=="Cancelled"){location.reload();}}});});</script>