Moving after separation

If a post nuptial agreement is in place but there is no “start date” would it have to be re-written as a separation agreement in order to have it start right away or just add a start date (day one of separation, June 18 2012 etc)?

If Post Nuptial does not say anything about moving then is not disclosing you are planning to move prior to signing anything that could void this private contract?

If you engaged in a new relationship after the official separation are there any “legal” consequences?