Custom Name or Removing Function Name For Pivot Table/Chart Data Columns

So does anyone know a way to do this? I am trying to prepare a series of charts and pivot tables are the best options because of the amount of data. My problem is simple the legend in the chart inherits the titles from the data columns, data columns inherit their names from the main datasheet plus the function used with the data.

As an example, I am charting water quality and I wanted to show three threshold values in the chart along with the actual data from the water quality sampling. In this example, I would prefer not to show the function used to draw a straight line, just what that line represents.

Any help would be appreciated!

Should be possible, take a look to the last paragraph Editing Pivot Tables

I read that also in the example used in the documentation the function is not displayed in the column header. However, I have found no way of not including the function.

Please attach a file sample to your question.

Example File