PCRE has builtin support for this kind of factoring, too:

  (?(DEFINE)
    (?<code>
      [A-Z]*H  # prefix
      \d+      # digits
      [a-z]*   # suffix
   )
    (?<multicode>
      (?: \( \s* )?               # maybe open paren and maybe space
      (?&code)                    # one code
      (?: \s* \+ \s* (?&code) )*  # maybe followed by other codes, plus-separated
      (?: \s* [\):+] )?           # maybe space and maybe close paren or colon or plus
    )
  )
  ( (?&multicode) )           # code (capture)
  ( .*? )                     # message (capture): everything ...
  (?=                         # ... up to (but excluding) ...
      (?&multicode)           # ... the next code
          (?! [^\w\s] )       # (but not when followed by punctuation)
      | $                     # ... or the end
  )