You can modify incoming or outgoing packets in this game easily and you don't even need a packet editor for it (+you don't have to bother with the encryption).
But it is not the client that is calculating your reward after the race so messing with outgoing packets is mostly useless and messing with incoming packets is just resulting in useless visual hacks as it is pointed out above.
A few cool things can be done by editing the packets, but mostly it is useless.
Here is an example for incoming packet:
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4AC0A01</a:ProductId><a:ProductTitle>GM_CATALOG_00000634,2</a:ProductTitle><a:ProductType>POWERUP</a:ProductType><a:SecondaryIcon/><a:UseCount>2</a:UseCount><a:VisualStyle>0</a:VisualStyle><a:WebIcon/><a:WebLocation/></Product><SoldFor>0</SoldFor><WasSold>false</WasSold></LuckyDrawItem></Items><NumBoxAnimations>100</NumBoxAnimations><NumCards>5</NumCards></LuckyDrawInfo>