If you are using a full node wallet as a backend, then yes, you can import a private key to your wallet.
Doing so will add any balance on that address to your hot wallet balance. (It will not affect any user balances, as there is no 1-1 correspondence between user balances and any addresses on your wallet.)
How you import private keys has nothing to do with the plugin. Consult the documentation of your wallet.
If your wallet is a Bitcoin core fork, then instructions on how to import a WIF private key using the importprivkey command are here and here.
Please let me know if you have any more questions.