Hmm..Aeros in a 172! Well in theory if you remain within the flight envelope of the aircraft you should be OK. Do not exceed G Limits VNE and observe restrictions at VMA.
However if you are attempting this sort of thing with no experience and are not in the care of a red hot test pilot/ aerobatic ace etc, then chances are that something vital will fall off. After all Mr Cessna produced a special version of the 152 (the 152 Aerobat) for this particular requirement so I would make a fair guess that the 172 is not cleared for aeros for a very good reason.
If an instructor is showing you - an inexperienced pilot how to have a go - he needs shooting and the aircraft needs scrapping. There are some fine aerobatic pilots in South Africa, I suggest you contact them via your national aerobatic association if you want to learn properly. As for the stall turn....well if you leave it too late and the conditions are perfect, then an inadvertent tail slide will be performed. In this situation, if you have not locked the rudders and control column very firmly, the controls will be forced rapidly to full defletion and break off. Go and feel how flimsy the rudder is on the 172 that'll give you something to think about. If you wish to live, I think you should desist. If you wish to learn about aeros, find a reputable instructor. In fairness to other users of the machine in question, you should pass your experiences on to the owner/operator (anonymously if need be)in order that the machine can be properly inspected.