What you propose will work but isn't the cheapest option.
Getting a foreign CPL just so that you can convert it to EASA is ALWAYS going to be more expensive than going straight for an EASA CPL.
Don't get me wrong, going to SA (or Canada or the US) is a great idea. But don't go there for a CPL. Get a PPL, get an IR and get at least 50 hours of PIC under IFR. Then come back and convert the IR and do a 15 hour CPL.
Do not get a SA CPL unless you intend to work in SA.