select regexp_replace(StringThatMustCorrected, '([A-Z])', ' \\1')
from TableThatMustBeCorrected

SQL> with t as (
  2    select 'StringThatMustCorrected' val from dual union all
  3    select 'ABC' from dual)
  4    select ltrim(regexp_replace(t.val, '([A-Z])', ' \1')) val from t;

VAL
------------------------------
String That Must Corrected
A B C

 SELECT replace(replace(replace(replace('StringThatMustCorrected','S',' S'),'T',' T'),'M',' M'),'C',' C') from dual;

REPLACE(REPLACE(REPLACE(REP
---------------------------
 String That Must Corrected

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.1.0 - 64bit Production
PL/SQL Release 9.2.0.1.0 - Production
CORE    9.2.0.1.0       Production
TNS for IBM/AIX RISC System/6000: Version 9.2.0.1.0 - Production
NLSRTL Version 9.2.0.1.0 - Production

SQL> with data as (select '&theText' theText
  2                from dual
  3               )
  4  select ltrim(max(replace(sys_connect_by_path(newLetter, '/'), '/')))
  5  from   (select case when letter = upper(letter)
  6                      then ' '||letter
  7                      else letter
  8                 end                            newLetter
  9          ,      rn
 10          from   (select substr(theText, rn, 1) letter
 11                  ,      rn
 12                  from   (select level as rn
 13                          ,      data.theText
 14                          from   data
 15                          connect by level <= length(data.theText)
 16                         )
 17                 )
 18         )
 19  connect by rn = prior rn + 1
 20  start   with rn = 1;
Enter value for thetext: ThisMightBeDoneBetter
old   1: with data as (select '&theText' theText
new   1: with data as (select 'ThisMightBeDoneBetter' theText

LTRIM(MAX(REPLACE(SYS_CONNECT_BY_PATH(NEWLETTER,'/'),'/')))
-------------------------------------------------------------------------
This Might Be Done Better