When you add any type of decoration to the blades, you could make it off balance. Also, when the fan is turned on, the spin of the decoration can have a psychedelic effect.
These "decorations" could also effect the function of the fan blades...in addition to the balancing issues. Remember the blade are acting like mini air plane propellers.
If you never use the "fan" option then it would work...but if that was the case why not just swap out the fan with a regular light fixture / chandelier?
My first thought is, "duck!" because the decorations might come lose and hit someone. With the speed of the fan, it could be a bad injury. Probably best not to add anything to a fan blade. I imagine if it were a good idea the manufacturers would have come out with all sorts of decorated models!
thank you for your comments, something to consider. but maybe i wont turn on the fan then what?