Cannot change formula separator

I have LibreOffice from PortableApps, under Win 8. I want to set the formula separator to “,” (cannot load image, not enough rep).

The default is “;”. I can type in “.” or “:”, for instance, but not “,”. Why? Can I accomplish what I mean?

ok. I tried what you want to do and it poses no problem on LO 4.4.4.3 running on Ubuntu 14.04.2.
I think it probably comes down to your locale setting. I have en_IE.UTF-8. What is yours ?

Hey Sancho, ¿ qué tal ?

I have a feeling - if I understand well, that this would be tantamount to changing the delimiter to something that would be ambiguous for Calc. Depending on your locale, , can be the decimal or the thousand separator. This is built in and therefore I suspect there is no way to actually use that symbol as formula separator. Did you investigate in that direction ?
-ced.