Change legend text based on measure/column

I would like to change "Comparison 1 Line" legend entry to match the particular comparison type for a particular row, so that the table may be filtered for a particular measure and have the corresponding comparison label, e.g. "Goal" or "National Standard." Is this possible?

I know I can use a card to return a certain field in the currently filtered row--would I need to create an image for the blue circle and create the legend item manually, or is there an easier way? (Some rows don't need the constant line comparison, so it would be nice to be able to hide the legend item when there is no data-- currently I just set the value to 0 if there is no data.)