A mature product has workflows, habits, and assumptions built up around it. Some of them are obvious. Others only show themselves when you try to change something customers have quietly depended on for years.
That makes the transition itself part of the product work. A cleaner new model can still create a rough experience if customers have to change too much at once.
Planning the transition
I try to get clear on where the product needs to go, then spend just as much time on how customers get there. The migration path usually needs its own decisions and tradeoffs.
Sometimes that means supporting old and new workflows for a while. Other times it means moving one behavior at a time or trying the new model first with customers who benefit from it most.
Current behavior is useful evidence. People have built real habits around the product, and those habits show what is valuable even when the model needs to change.
A transition is going well when customers can adopt the new model without having to relearn everything at once. That usually takes longer than a clean redesign, but it creates a lot less unnecessary disruption.