Editing transitions.ini requires no special hacks that would require thinking of Theme Customizer To OP: I suggest you code it to follow this pattern: - check if transitions.ini exists under /etc/hildon/theme/ => if exists, edit that ==> else edit one under /usr/share/hildon-desktop/ That way your program will work with any enviroment. If user then chooses to switch theme which does not have custom transitions, he needs to re-run your program to get the results. Other way would be to edit transitions.ini in both locations if they exist. No need to look for non-standard folder like /opt/theme-customizer/ etc.