Question about fx impact fixed shroud

I did that very thing many times without any issues. 
All the stackable shroud pieces are the same design. The only difference is the size of the hole in the end cap. 
If your swapping back and forth between end caps, just be sure to mark them in some way. You don't want to try to blast a .30 through a .25! It'll destroy your accuracy! lol :)

Note: There is a smaller diameter stacked shroud system that is used on the Streamline. These sections look more like cups than tubes. I would not attempt this with that system. 
Easy to tell the difference... Are your extensions hollow tubes (larger Impact style) or cups (smaller dia style).
Tom