Assume that you have the following model, and the chart has two states:
Suppose that you want to edit state A separately, while someone else is editing state B. You can convert state A to an atomic subchart for storage in a library model. After replacing state A with a linked atomic subchart, you can make changes separately in the library. These changes propagate automatically to the chart that contains the linked atomic subchart.
Right-click state A and select Group & Subchart > Atomic Subchart.
Create a new library model.
Copy the atomic subchart and paste in your library.
Save your library model.
In your main chart, delete state A.
Copy the atomic subchart in your library and paste in your main chart.
You can now edit state A separately from state B without any merge issues.