The question that you asked was:
> when the leader is elected every 10 minutes, do they get a choice of what block they append to the chain?
and the answer is yes, the miner that gets elected chooses which transactions to append to the chain. Do they pick the transactions after getting elected? No, they pick them before getting elected. In fact, it doesn't matter whether they pick the transactions before or after getting elected, because their chances of getting elected are unaffected by which transactions they picked. Therefore, it makes absolutely no difference. The fact that you think it makes a difference tells me you're very confused about the role miners have in the bitcoin network.