This is a very interesting scenario.

I also have an NW ticket, to Africa next month,
and now would like to modify the return without fee,
but the sked changes so far are more
like 30 mins, not 2 days.

In most ways. this is a lucky break for you.
Clearly, don't push it too close to departure.
j
Just take some time, decide what works for you,
and enjoy the free change !