I implemented this. However it is not quite as straight-forward as it sounds, because here in (continental) Europe we use "1.234,56789", while the US (and others) use "1,234.56789". Forutnately there are already build-in methods in C# for this.
Important notice: Do not post style.ini files publically that use thousand separators or non-integers! If someone else in another country downloads it, the editor may no longer be able to parse the file due to different expectations regarding the number formatting.