Yes, it is possible to import products yourself and pay for excess baggage to save on freight and using a clearing agent. However, if you are importing a large quality of stock, and as you have an importers code all you would need to do when you arrive back in South Africa is to declare the goods and pay VAT.
Check requirements before you leave South Africa
But every importer needs to understand the customs procedure for clearing imported goods. SARS is very helpful and you should call them and check that you understand what paperwork is required on your return.
One of the documents you must have is the original invoice for customs when you arrive in South Africa. SARS requires a full description of the product in order to check the details for you.