Hi Edi,
As per the standard SAP, once you have assigned characteristics and values fields to your operating concern (KEA0), you can't de-assign them. When characteristics or values fields are in assigned status, you can't delete them.
But I hope there won't be much problem of having that characteristic also. If you look at performance wise, then instead of deleting, make "not used" under profitability segment characteristics, remove from the characteristic groups etc. While doing so, please check any derivation rules written based on these, or any assessment cycles defined with these also..
Regards...
Jose