So, technically, yes... you /can/ delete.

However: Do the relays honor that? Does the delete request reach enough relays to propagate across the network? Chances are a blastr relay has sent it into one random af corner of the internet and at some point propagates the event right back into the network.

tl;dr: Don't rely on it. If you have only just posted it and immediately send the delete request you MIGHT be lucky. Might, perhaps, potentially.