Can I use candle wax to finish leather edges instead of beeswax?

Candles are usually a mix of bees wax and paraffin wax so you absolutely can use candles as a substitute. An even better idea and a real money saver: get a pure beeswax candle and use that. Beeswax softens at body temperature and is a much softer and more flexible wax. Paraffin wax can turn flakey, dry and hard. Beeswax soaks deeper into the leather while harder parrafin stays more on the surface. Beeswax offers some waterproofing properties, so does paraffin but because paraffin it sits on the surface protection isn't as good. Beeswax also give a warm soft glow when fully buffed into the leather. Paraffin never looks as soft and warm or glowing.

Instead of an expensive lump of wax from the leather craft store get a beeswax candle. It's cheaper and works just as well. You can also poke pins and needles into the wax to help them slide through the leather. You can also use the wax on thread for hand sewing: draw the thread through the wax, use a clothes iron to melt the wax and embed it into the thread and it will easily slide through the leather.

You can use whatever you want, but:

You have no information or control over what the "candle wax" is made of. Most are full of synthetic additives.

You know what's in beeswax.