declare
    column_exists exception;
    pragma exception_init (column_exists , -01451);
begin
    execute immediate 'ALTER SESSION SET NLS_NUMERIC_CHARACTERS = ',.'';
    exception when column_exists then null;
end;
/
declare
    column_exists exception;
    pragma exception_init (column_exists , -01451);
begin
    execute immediate 'ALTER TABLE PARAM_RECOLECCION MODIFY (IMPORTEADICIONAL NUMBER(10,2))';
    exception when column_exists then null;
end;