Colour (option between custom static and changing depending on the value of your ping)
Position
Size
Alpha
How to change the settings:
In the mod folder, navigate to mod\scripts\vscripts\. You'll find a file called s2_ping_display.nut there, open it with a text editor (normal notepad will do)
On the first couple of lines you'll see a struct called settings, each of the options have a description, change them as instructed
Save the file and start your game/click reload mods in the mod section, your changes should be applied