Is it possible (in some way or other) to expire a txout?
Expiring a txout doesn't really make sense, since it would destroy the coins, and there is no way to destroy coins. (Coins not spoken for by any txout are contributed as fees.)

You could create a transaction with a lock_time in the future that sends the coins to another bitcoin address. If you give this transaction to a counterparty, they would then have the option to broadcast the transaction to the network after it becomes due, and it would take effect.

Before that time, you could create another transaction without the lock_time restriction, move the coins, and make the counterparty's transaction useless.