The only other change you need to make is if you don't want the hidden field to be sent with the rest of the data in the form when the form is submitted. If you are the only one who will be receiving the form then it isn't going to matter but if you are sending the form to someone else then you may want to remove these hidden fields from what is sent to the server when the form is submitted as well. Doing that is also simple since all that you need to do to achieve that is to remove the name addtributes from those fields (or if you don't want to remove the name attributes then change all the names of those fields to the same name as the submit button uses).
Note that the option of removing or changing the field names will only work with the newer version of the script that reference the fields by their id rather than their name. You can't change the field names or remove the field names in the original version of the script.
This article written by Stephen Chapman, Felgall Pty Ltd.