The ability to edit Oracle Homes : LOCAL, NLS_LANG, ORACLE_SID and SQLPATH is missing in Toad for Oracle version 12 and later.
This ability was removed due to the settings of the parameter are closely associated with Oracle.
These are settings that typically do not change once set properly the first time so it is best if the user configures their home(s) according to Oracle specs.
Hence, the ability to edit these parameters was removed from Toad.
WORKAROUND