When to season popcorn?
I worked three years in a movie theater in my early twenties.  The butter is tricky.  We would microwave it then separate the water from it.  If the water is still in the butter and put on the popcorn the water will make the popped corn soggy and give off an unappealing smell.  We would usually pour it off to separate them but that works best when a large amount is used.  A small amount could be warmed in a pan long enough to evaporate the water.  then alas put it on the finished popped corn.  Time it so both the corn and butter are warm at the same time.  Don't cover the popped corn with the idea of keeping it warm; There is still a little moisture in the popped corn and will make your treat less crispy.
If dried spices are the idea then try infusing the spice with the butter after the water is removed.  Don't get the mixture any warmer than warm.  You don't want the spices getting browned.  If the spices were put in the kettle while popping the corn they would be too toasted.