Does adding a motorized fan to a hot air balloon change its class as an aircraft?
Well, a balloon already is an aircraft, specifically:


  A balloon is a lighter-than-air aircraft that is not engine driven, and that sustains flight through the use of either gas buoyancy or an airborne heater.


So if you were to attach engine-driven propellers to your balloon it would no longer be a "balloon". It would start to sound a lot more like another kind of aircraft -- an airship:


  An airship is an engine-driven, lighter than air vehicle that can be controlled in flight.


So from a licensing standpoint there would appear to be two major considerations: First the pilot of such a chimera would need to be licensed to act as pilot in command of an airship (not a balloon), and second the modification itself would have to go through appropriate regulatory channels, since it is changing the fundamental nature of the aircraft in a way that would almost certainly attract some scrutiny.



Specifically regarding the fans/propellers you're talking about, it looks like those are intended for use as inflation fans to help you out when you're setting a hot-air balloon up - once you've got the envelope inflated and the heater is doing its job you don't really need the fan anymore, and you would leave it with your ground crew.

As far as I can tell they aren't intended for use as engines for moving and steering a balloon - I suppose you could carry one aloft with you if you were feeling bold, but I'm not sure what the impact of doing so would be from a regulatory standpoint when it's not permanently attached to the balloon, and I'm not sure how effective they would be as propulsion with only a few horsepower behind them.