Can I restrict the form users to submit the form just once and also allow them to edit their submission entries?

I host a best business competition in my city and I want to know if jotform can handle this type of form. 

1) Users may only fill it out once. I know there is a security setting and only 1 IP address can fill it out. Are there other security measures I can take?

2) Users can come back later and change their answers and so to speak lock and unlock them.