I wonder if this is possible. I want to show the text (numbers) of the scale bar in Print Composer with a thousand separator in order to make the labels more readable. All I can do for now is change the font and color. I can not find an option similar to the grid labels, where you can define a custom setting for the label and use format_number(@grid_number,0 for instance. I am using QGIS 2.18 in Win 10.