/usr/share/plasma/plasmoids/org.kde.plasma.kickoff/contents/ui/FullRepresentation.qml

This is the file you want to edit, lines 31~34. Make sure to not mess it up because it may break your Plasma Desktop, but if you only change the values it’s okay. Keep in mind that at the next update it will be resetted and your changes will be lost, you may want to backup your modifications or something like that, or perhaps create a new plasmoid inherited from this with only your changes (I’m not 100% sure this can be done)