Just rename the blunder buss to something
irrelevant and put the crobo gun
where the blunderbuss was and name
it with the same instance name as the blunderbuss.
Same goes for actors. Just name them after the originals,
and name the originals something else, and make you actor load before the the original one.
Have a nice day.
EDIT: This mod tells you how to do it better and comes with an actor to replace with.
viewtopic.php?f=23&t=5786&p=103393&hilit=brainhunter#p103393