I was wondering if I were to book the exact route I wanted for November 2017 at pre-devaluation prices (120k pp return), whether after paying the change fee for change of dates, if they would also charge me the difference in miles due to the devaluation? I would prefer to lock in at the lower rate, however not possible for the dates I’m looking at.
The Points Guy has produced a detailed overview of this very point which is well worth a read.
In short, route changes would need to be repriced, but date changes should stay at the same price. Risk is the route you want isn’t available for the dates you want, but worst case scenario, you’d just pay the cancellation fee or pay the extra miles for rerouting.
[Sorry for a delayed reply. I blame Christmas!]