You can in libreoffice, but not excel. You _must_ change your locale. I went down this rabbit hole a few weeks ago trying to open some Dutch datasets.
Also, I believe you can change the default separator in Settings somewhere.
I tested semicolon and comma and in both cases the autorecognition selected the correct delimiter but I could change it to equal sign, space, tab, user defined.
You can't change the decimal separator, but the field delimiter is possible.