You can create custom number formats in Excel, and can base them on the existing formats rather than start from scratch.
If you select one of the cells that appears as close as you can get it and choose, from the cell format list shown above where "Accounting" is selected, the "custom" entry that appears at the bottom of the list, you can edit the format code that Excel uses.
All you need to do is to swap arounf where "." and "," appear in the format code and you are away.
I haven't used them very much for years and you shouldn't really need to know the details for a minor change but to get you on your way if you want to do anything fancy here's what I remember about the codes (which may not be correct but you'll get the flavour): there are four parts to the format code; what appears when the number is positive, negative, zero and text. "_" shows a space of the width of the following character, "*" instroduces a fill of the following character, "#" stands for any digit etc