Great question. This issue is addressed in the Warranties section of the rules. As long as you retain the rights to submit the app, there are no other limits on submitting an existing app - of course, you must be sure to include at least one of the eligible datasets. Good luck!
Here's the relevant section from rules:
By submitting an Entry, you represent and warrant that all information you submit is true and complete to the best of your knowledge, that you have the right and authority to submit the Entry on your own behalf or on behalf of the persons and entities that you specify within the Entry, and that your Entry (both the information and software submitted in the Entry and the underlying technologies or concepts described in the Entry):
(a) is your own original work, or is submitted by permission with full and proper credit given within your Entry;
(b) does not contain confidential information or trade secrets (yours or anyone else’s);
(c) does not knowingly, after due inquiry (including, by way of example only and without limitation, reviewing the records of the United States Patent and Trademark Office and inquiring of any employees and other professionals retained with respect to such matters), violate or infringe upon the patent rights, industrial design rights, copyrights, trademarks, rights in technical data, rights of privacy, publicity or other intellectual property or other rights of any person or entity;
(d) does not contain malicious code, such as viruses, malware, timebombs, cancelbots, worms, Trojan horses or other potentially harmful programs or other material or information;
(e) does not and will not violate any applicable law, statute, ordinance, rule or regulation, including, without limitation, United States export laws and regulations, including, but not limited to, the International Traffic in Arms Regulations and the Department of Commerce Export Regulations; and
(f) does not trigger any reporting or royalty or other obligation to any third party.