In what sense would I want to translate these preferences?

I think in the sense that the new world-model ought to add up to normality. The move you propose probably only works (i.e., is intuitively acceptable) for someone who already has a strong intuition that they ought to apply empathy and population ethics-type reasoning to all decisions, not just those that only affect other people. For others who don't share such intuition, switching from "unique thread of experience" to empathy and population ethics-type reasoning would imply making radically different decisions, even for current real-world (i.e., not thought experiment) decisions, like whether to donate most of their money to charity (the former says "no" while the latter says "yes", since the difference in empathy-level between "someone like me" and "a random human" isn't that great).