I've searched around a bit and I couldn't find anything related to it, but is it possible to change the combo numbers at the bottom left? If so, what would the filename be?
Since the 2.4 skin version update you can customize the combo counter numbers individually. Just make numbers from 0 to 9 all with the same prefix (e.g. combo-#.png) and add the following to your skin.ini under the fonts section
[Fonts] ComboPrefix: combo
The normal score font set is used by default since there is no new font for it and would break older skins which don't have a custom combo font.