WITH
  TMain AS(SELECT 'A-Za-z0-9А-Яа-я+-.,:;* ()=?%/ўіІЎЁё' AS charSet FROM DUAL)
SELECT regexp_substr('/MARK/213213213AAAasdsadsa', REPLACE('/MARK/([^(AAA|BBB)][<CharSets>]){1,35}', '<CharSets>', charSet))
FROM TMain;

...
WHERE строкa NOT LIKE '/MARK/213213213AAAasdsadsa%'
          AND....
...

WITH
  TMain AS(SELECT 'A-Za-z0-9А-Яа-я+-.,:;* ()=?%/ўіІЎЁё' AS charSet
                  , '`'                                 AS charChange 
           FROM DUAL)
SELECT regexp_replace(REPLACE('/MARK/test12aAAA9sdsadsa', 'AAA', charChange)
                      , REPLACE(REPLACE('^/MARK/([<CharSets>]{1,35}[^AAA]).+$', '<CharSets>', charSet), 'AAA', charChange), '\1')
FROM TMain;