If it’s currently wired as a non-networked three-way, then it isn’t going to work to just replace one device . You have to replace all of the devices in a three-way, not just the master.

Brand new to Smartthings and trying to get some areas of the house “connected” ASAP. Most of the devices available are intuitive enough to figure out, but one area that seems to be a bit confusing is the on/off light/scene/etc. switchs that are available. I am mainly confused with the 3/4-way options, the add on switches and how these inter-operate with existing switches (if at all). My initial understanding is that I can replace a single pole switch with something like the GE Z-Wave Wireless Lighting Control On/Off Switch, if I want it to be able to dim the lights I need one that supporting dimming. If I have a 3/4 way lighting setup I need to get a zwave/wireless switch that is capable of supporting 3/4 way. However does this mean I can just replace one of the existing switches with…
So you can use the DZ6HD as a standalone switch, but then there have to be no auxiliaries wired into the circuit.