Yes, I do this. I have worn Filson gear for many years and my jacket and pants require re-waxing.
I have tried other products and homemade mixes (melted beeswax, toilet wax ring) besides the tins of Filson wax but I have come back to using Filson wax .
I have a favorite Carhartt vest that is the tyical Carhartt cotton duck material that I also wax. I make sure it is clean-ish (never washed in a machine or even hand washed) first, and warm. Once you wax a piece of clothing you can't ever wash it with soap again. I have pants that are more than thirty years old and have never been washed. I'm most proud that they still fit. Also don't wear it in your car or you might get some wax residue on your seat.
I'll lay an old towel on my ironing board and rub in the wax in small areas, slowly covering the entire vest. Rub it in really well.
I don't use a hair dryer or anything like that, just lay it out to air dry overnight before wearing it.
The look is a little wild. It doesn't take the wax quite as well as the Filson material, but the more you do it the better it looks, although better is a relative term. It doesn't look bad, just different, and I've actually gotten compliments on the vest because it does stand out a little.
I find it really helps keep the constant rain I'm subjected to from soaking through the shoulders, especially. It's no substitute for real rain gear, but for use in a non constant downpour it's good.
You can order Filson wax online but they charge a shipping fee. You can order it on Amazon with free shipping but they raise the price so it's the same. I buy mine locally at a work clothes store. The logging supply shop near me has stopped carrying Filson because loggers aren't really wearing it anymore, it's becoming more of a boutique brand, straying from it's roots.
One more thing, the waxed garment tends to stiffen up when cold, this is not a bad thing in the field as it tends to make it feel a bit like armour, while retaining good field of motion. Don't store it outside in the cold or it will literally stand up in the corner.