If your intentions is to get the C208 rating on your CASA license whilst completing training in Johannesburg so that you can use the CASA validation to fly a Botswana registered aircraft I doubt very much you would be able to do such a thing. Although not 100% sure.
The only way I can think that would work is if you gained a South African CPL, gained the C208 rating on the South African license and then got the rating placed onto your CASA license (I think that is about $150 and simple paper work, which CASA will send an email to the SA authority to confirm the rating). Or just validate the SA license in Botswana.
To gain the SA license you would need, flight planning exam, Met exam, law & procedures exam, medical and IFR flight test ( which you could probably do as part of the rating).
I don't know much about the new part 61, so perhaps I am wrong about this.
Goodluck