When a new lead is added to Salesforce due to the integration - I want to merge it with an existing contact, while maintaining the Swift person ID what do i do?

Salesforce allows multiple duplicates in both leads and contacts. Whenever there is an entry introduced from a SD/SF integration, Salesforce accepts the new member as a lead. If you know that this new lead is in fact a contact, do the following: 

•  Convert the lead to a contact and then using Duplication Manager merge those contacts, making the one with the Swift person ID the winning leader of this merge.