Can you convert an above ground 24' round pool into an oval above ground pool?

Answer is no

You can remove a round one and install an oval after, of course, you make necessary adjustments to the ground--making the ground level in an oval instead of a circle. The only things you might be able to re-use from the round pool are the pump/filter, ladder, skimmer and return fittings, and your cleaning equipment. Round pools are built quite differently and are not meant to turned into ovals. Theyndon't have the supports required, whether that be braces or straps. So, basically the answer is 'no'.