Moving your stake
You do not have to unstake to change your mind.
Moving stake to a different validator on the same subnet is not a trade. Your alpha stays alpha, so there is no swap fee and no price impact. The small network transaction fee that most actions on the chain carry still applies.
Moving stake to a different subnet is two trades: your alpha is sold for TAO, and that TAO buys the new subnet's alpha. Each leg can have price impact, so check the quote first.
Transferring stake is different again. It moves a position to another coldkey, which means giving it to someone else. Treat it like sending TAO: check the address carefully, because it cannot be undone.