Will changing the contact for a work item in the app affect its link to TSheets?

A change of contact will not break the connection between TSheets and Intuit Practice Management powered by Karbon, but the work item within TSheets will not be found under the new contact (it will still be displayed as connected to the old contact). Therefore, you will need to move the work to the new client inside TSheets as well. If you don't do this, TSheets will continue to report the work item under the old client.