- If you create a private key using a cold wallet like Trezor, Ledger, etc., and then you import that private key or mnemonics into a hot wallet, you basically defeated the purpose of a cold wallet.
The mnemonics generated by your cold wallet should stay secret at all times, stored in a safe place.
You could keep all or most of your balance in a cold wallet, and then transfer some or little balance to a hot wallet to use on a daily basis, knowing that if you lose it would not be a big deal.
- If you create a wallet/private key/mnemonics using a mobile wallet and then you export that to a cold wallet, it could work, but I wouldn't trust that so much.
Your most important private key or mnemonics should never see the light of the day. And copying it from a hot wallet to a cold wallet, and from a cold wallet to a hot wallet, may compromise it. So, be very careful.
As I said, you could have little balance in hot wallets, and most of your balance in a cold wallet. You can have as many wallets as you need, so you can transfer some balance from your cold wallet to your hot wallet to use on a daily basis.