How to spend from the "master_private_key": “df484533kf5mzv83892a234a44ae9z83m832987a82mqwmdkks018121204v95las9" I made a backup of an outdated command line interface BTC wallet, here is an example:
"master_private_key": “df484533kf5mzv83892a234a44ae9z83m832987a82mqwmdkks018121204v95las9"

How can I import this key into another wallet?
While you may be able to import the key into another wallet, it is better to create a new wallet with a new key and transfer all the bitcoin out of the old wallet and into the new one by making a regular bitcoin transaction on the blockchain. This eliminates all sorts of possible complications, including the security risk of disclosing the keys from your old wallet.