Hi Jason,
Indeed, this chart cannot customize Series. It's the same in my environment.
So we can import a new chart while retaining the original chart.
Here are the steps:
1. Export the original chart. Then change the name of the original chart.

2. Open the exported original chart file. Then delete the three pieces of code. (Delete the area selected by the red box in the picture.)

3. Import this file. Keep Both.

In this case, the original chart still exists, and the new chart replaces the original chart.
