Imports, not re-typing
Parties, ports and charges come in from the sheets you already have.
Nobody switches mid-shipment. This is the plan that respects that: live jobs finish where they started, new jobs start in the new system, and the sheets retire by attrition.
The failed migration everyone has heard about tried to move everything on a weekend. The one that works runs both systems for a month and lets the old one empty itself.
Parties, ports and charges come in from the sheets you already have.
Live jobs finish where they started. Nothing is re-keyed mid-flight.
Your fallback remains untouched until it empties itself. That is the safety.
One real quote with the margin visible before sending — the moment the switch pays.