Hi!
I think once the stake certificate registered the stake address is fine even the stake keyDeposit changed. The stake certificate can be de-registered and it will automatically gives back the stake keyDeposit.
this is the command how to de-register:
cardano-cli stake-address deregistration-certificate
I think 2 ADA does not need to be provided when building the transaction…
That case the 2 ADA should arrive to the stake address (just like in case of pool de-registration) where it can be withdraw from
https://docs.cardano.org/projects/cardano-node/en/latest/stake-pool-operations/withdraw-rewards.html
but I will verify this by creating a de-registration soon…