Yes, you can tune almost any yo-yo with a setscrew axle, even if that setscrew was bought from a hardware store. Why buy axles from a hardware store instead of YoYoJam? Well, first off, they are cheaper. At a hardware store they cost about thirty to forty cents each. Secondly, you can get shorter axles. I really dislike how long the YYJ axles are; they make it take quite a while to screw the yo-yo together. Finally, from my experience YYJ vibe comes from their axles. The setscrews I’ve gotten at the hardware store have absolutely no vibe, without tuning it at all. Now my Lyn Fury is as smooth as my Superstar and that isn’t an exaggeration.
I will warn you, the adjustable gap feature comes from some coating or machining process on the YYJ axles. That means when you use a setscrew from a hardware store as your axle, your yo-yo will no longer have the adjustable gap. Some people really like the adjustable gap, I don’t, so it is a plus in my book. If the gap is too small for your tastes you can always use shims.