Create prefix list from learned peer routes

This feature unfortunately does not exist, would be great if it did though. Have you logged a feature request?

NB: The more people individually ask, the more likely Mikrotik will listen…

Have a look at the following, appears that it may do what you’re looking for:
http://forum.mikrotik.com/t/automating-address-list-maintenance-manrs-compliance/115375/1