Simply put, this is not a good idea. The offer to purchase is a binding contract, and withdrawing from it will incur penalties.
However, you can withdraw an offer to purchase if certain clauses in the contract have not been fulfilled.
For example, when you sign the offer to purchase, you can include a clause that exempts you from the purchase if you have not obtained home loan approval by a certain date.
The only scenario in which you can withdraw an offer to purchase without a clause in the contract being broken is if the property is worth less than R250 000. And even in this case, you can only do so within five days of signing the offer to purchase, and you must provide the seller with written notice.