I have a "patch" file that I copy to every new game I play which sets the defaults I prefer.
You need to do it before you play the game for the first time, but other than that - it's simplicity itself.
Maybe you could adapt it to your own default preferences?
Python:
default preferences.text_cps = 36
default preferences.afm_time = 8
init 990 python:
config.developer = True
config.console = True
config.default_music_volume = 0.15
config.default_sfx_volume = 0.5
config.default_fullscreen = False
config.keymap['toggle_afm'].append("alt_K_PAGEUP")
preferences.afm_time
is the auto-forward timer.
I'm also switching on developer stuff, setting my preferred music volume and adding a keybind to toggle auto-forward off and on for all games (including those that hide the quickmenu).
It works 99% of the time, but every so often I come across a game where the dev has REALLY gone out of their way to mess with the RenPy internals.