I am considering finally splurging on DONEX ex-JNB to bridge an existing gap between two tickets and cover my travel next year. My first segments is JNB-MAD, but after that I really don't have a set itinerary. I was wondering could I do dummy segments to fill out my itinerary, then later on do more than just date changes but also re-route per my plans and only incur the up to $125 change fee with no repricing etc?

Example (after JNB-MAD, assuming OW flights actu)
Go from MAD-DXB/DOH-LHR-LAX to MAD-HEL-LHR-SFO
Go from LAX-DFW-JFK-YVR-ORD-DCA-JFK-HKG to DFW-YVR-JFK-SJU-DFW-HKG

and so on.

I am thinking of initially putting in some basic segments to route Africa-Europe/ME-North America-Asia-Africa. Then later making changes as I plan to visit each continent, meaning 3 major routing changes. Is this a viable plan or am I expecting too much flexibility and should rather choose my destination points now and stick to the date/time changes only?

Thanks in advance.