Hi Jon,
Your best bet may be to convert the legend to graphics and individually edit the elements of your legend by making parts of the text element bold. I believe text elements will implement html formatting, so perhaps use the <b>Text</b> tags to make the text bold.
I'm not sure how many unique values you're trying to show in your legend, or if the pieces of text that you want to make bold fit a certain pattern, but if you break the legend into individual layout elements you may be able to conditionally make them bold using the arcpy.mapping TextElement object to apply the changes.
Perhaps something like:
import arcpy
mxd = arcpy.mapping.MapDocument(r"C:\Project\Project.mxd")
for elm in arcpy.mapping.ListLayoutElements(mxd, "TEXT_ELEMENT"😞
if elm.text == "AA - BB":
elm.text = "<b>AA</b> - BB"
mxd.save()
del mxd
Let me know if you find a solution! One of my colleagues occasionally has to perform similar operations on map layouts and would be interested in the results of your effort.
Warm Regards,
Micah
