Changing data sheet column header font size

I’m pretty sure that this can be done, but how?

I’ve searched everything I can think of without success. Tried to find the data sheet blueprint to change it there, but this blueprint doesn’t seem to be available to users.

Sorry, you cannot find it because there is no option to change the size or font of the column header text. The data sheet uses Apple’s NSTableView class which does not provide options to modify the header.