re: Has anyone thrown a Boston butt into the crawfish pot after the crawfish is done?

No, but I've done a corned beef that way at a crawfish cooking comp. and you had to have something totally different to add after the boil to add to the pot.

So I did one of those store bought corned beefs already seasoned and ready to cook.

Came out great. A Boston Butt would take a hell of a lot longer due to the size of the chunk of meat if put in whole. I'd rather smoke that bugger.