Generally not a good idea, because the lights, fuse and wiring are complementary / sized to match each other. Increasing the power draw without increasing the wire size could be a very bad idea. You're talking about adding ~9 amps of load / draw / demand to the existing circuit (watts = volts x amps) . If you are adding the lights to the fog lamps circuit, what is the power rating / draw of the fog lamps. Add that to the new lights and look up what wire gauge and fusing you should use for that load and see if your existing wiring meets or exceeds that. Only if it does should you attempt your idea of just adding the new lights to the existing circuit.
It's really quite simple to add a proper wiring / switch / relay circuit, to either an existing fuse panel or direct to the battery or a new additional fuse panel. And not difficult at all to learn the basis. Ideally you have a relay involved in the heavier duty circuit, with only minor power / wiring leading off from the relay to the dash switch location.
