Correct me please if i am wrong…! Assuming we start from the Daedalus platform (4.0.5) - no experience with Trezor:
1- a wallet is just a functional graphic user interface, to manage a specific asset and some other funcionalities associated with that asset (or several assets) - meaning that your assets, rewards, etc… are in fact running in the blockchain. So if you keep the private key of that “wallet” safe you allways will have access to your assets from any compliant “wallet”.
2- “restoring” your Daedalus wallet in a different “wallet” (third party GUI to manage your assets) is not a transaction. Pairing wallets do not envolve transactions (?). At least with YOROI there is no transaction involved - you can even run different Wallet platforms at the same time and they just will eventually sync.
3- There is no Undelegation button in Daedalus. In some forums I read that this is temporary. It had one before but not anymore. Yoroi do have that functionality.
4- Withdraw funds in order to get back the 2 ADA delegation deposit, and ALL the rewards due to one’s balance, shouldn’t lead to some strategy, because other wise you will lose 2 epochs of rewards always staked in advance ? Of course depending on how much important those rewards are.