Originally Posted by cnc2002

I'm looking to book a SM award in J for March/April 2018, and dates in that window are starting to open up. I'm platinum so there's no cost to re-depositing the miles as I go through multiple reservations to get my preferred dates.
If I search for a one-way to JNB or CPT, from JFK or BOS, the fees/taxes are between about $6 and $55. When I look at one- way returns on the reverse routing, fees are about $800-1100 per person. These include routings through both LHR and CDG. However, if I set it up to book a roundtrip, this drops the fees to around $100-200.
Is it possible to book the outbound portion when the dates become available (~331 days out) and then, when my preferred return dates open up, grab the original one way outbound and combine it with a return so that the taxes are reduced dramatically? Or would I have to book the roundtrip separately (if the low 95K fares outbound are still available) and then cancel the outbound one-way routing? If I were to cancel the outbound one-way reservation and then book round-trip, will the cancelled seat be put back into the inventory right away, or does it take a while?