Personally, I would say no. I know there are supposedly plug-ins, but they don't make much sense to me as they are poorly documented. Basically you need to understand Python (which frankly, I don't).
And if you buy from B&N, apparently the encryption they use is tied to your credit card. So to decrypt it, you need to give out your CC number, which is not going to happen as far as I am concerned.
Beyond that, there is a design feature in Calibre that for some reason makes the left margins gigantic when you convert certain epubs to mobi.
https://www.mobileread.com/forums/sho...&postcount=330
And as I guess it's intentional, it's never going to be fixed.