If we haven't decided what morality to use yet, then how are we making moral decisions now, and how are we going to decide this later? I think that what you might call "the function that we'll use to decide our morality later on" is what I call "my morality both now and later".

Or you might simply mean our morality will keep changing over time (because we will change, and the environment and its moral challenges will also change). That's certainly true.