Need to modify some X-axis labels in pivot chart

Hi, In the sample pivot-chart I've attached, I'd like to modify only some of the X axis labels. For example, I'm looking to highlight the major column headers in bold: L2, L3, L4, etc., while leaving the sub-column headers (Alfa, Citroen, Dodge, etc.) in regular font.

Similarly, can the major X axis ticks be modified while the minor ones are not?

Thanks,
Mike