(1) Is there any way to apply retention analysis to user properties retro actively?

Example: we just introduced a form to track the users “hair color”, and i would like to do a retention analysis and group by the user property hair color, but also for the time before we introduced this property (which would be an assumption that whatever hair color the user has today, they had it from the very beginning)

(2) What if the hair color of a user changes over time, how would he be included in the retention analysis? E.g. he had “hair color” = “black” in the first 3 months of his lifetime, but then changed to “blonde”?