I have a "manually" sketch for relay, you may add any number of relays, choose the PINs you want on Arduino. Of course you are limited by the type of the board you are using. You just have to copy/paste the same code and change the relay number 1, 2, 3, 4 etc: https://github.com/Mihai258/HomeAssistant-MySensors-MQTT/blob/master/Single sensor/MySensorMQTT_REL/MySensorMQTT_REL.ino
Of course you have also to take care about already used PINs (some of them are used for the NRF24 module, some for LEDs if case etc).