Absolutely, it is possible. An ssh connection via wifi gives you full access to the gpio pins which can then control relay boards. You can control the pins under program control, or directly with simple text commands. It is important to protect the GPIO pins from potential EMF spikes generated by the relays but the commercially available relay boards you can buy from the RPi vendors are usually optically coupled to the GPIO pins. There are plenty of tutorials on using relay boards online, so let a good search engine like google or Duck Duck be your friend. In general, the complexity is no greater than what is required to control an LED and that is a good place to start learning. The tutorials on this web site are excellent and easy to understand.