Question about Connection and Allomancy

So, I was thinking about twinborns and noticed I dont really know what filling a duralumin mind does.

Can you stop people from affecting you with, say, mental allomancy if you start to fill your duralumin mind? Since you wont have connection to the person anymore?

In that same vein, will you even be able to use allomancy at all since you presumably wont have a connection to Harmony anymore?

Thanks for the answers in advance.