What is the recommended way to swap hash consistent servers (with least sudden hash change)

If I have the following config

upstream ImageCluster {

hash $cachekey consistent;

and wish to swap to
would it be better to delete, restart and wait for the hash
to update,
add and then restart,

or just delete and swap with all at once?

Also do you think it’s a good strategy to add weightings so I can slowly
decrease the weightings value and restart nginx serveral times until the
weighting becomes 0, so that it will slowly change the keys?

Thank you.