hi,
Sorry, this is currently not possible. Only the settings which are listed in the filetype definition files(filetypes.python and so on) are available. As a workaround you could use two different configuration directories for Geany. Maybe the default one in ~/.geany/ for usual files and a another one, maybe ~/.geany_py for your python files. Then start Geany as usual for normal files and start it with geany -c ~/.geany_py/ for your python files. I know this is not a very good solution but it would help for the moment.
Well, that's a possibility. Might this be implemented in the future?
maix