Well it can be done, if the phone is running Marshmallow. But, that isn't something Samsung controls. That is through Google, who makes the Android OS. Also, app creators themselves can make it so an app doesn't run on a card. However the info you listed, about the watch, is a totally different thing.
Since your phone is running Marshmallow, you should be able to make the change, for many files. Just change the sd card to read as Internal rather than External. BUT I would suggest doing that only with a clean/empty card. So back up the files you have on it already, or move them to the phone, then reset the card, and then you should be able to do more.