I changed a line the file Packages\Python\Symbol List.tmPreferences:

  s/class\s+([A-Za-z_][A-Za-z0-9_]*.+?\)?)(\:|$)/CLASS $1/g;

In Sublime Text 1.4 I get what I expect.
But In Build 2027 the regex substitution in Symbol List.tmPreferences seemed to be ignored - at least for Python files. Why?