I am really confused

I need to transformate coordinates from one given system to another.
I have updated the data in the table MDSYS.SDO_DATUMS but it seems to me, that the data is never getting touched. Even if I change the name of ex. European 1950 to ED50 it doesn't seem to make any harm (or good).

Are there another table like MDSYS.SDO_DATUMS which is beeing used by the table MDSYS.CS_SRS ?

Please help!