1 - you can't. that just doesn't make any sense at all... unless the directory is inside /home. you could always create one in there and create a symlink to it from somewhere else though, if that's good enough.
2 - very carefully and slowly if at all. you can for example copy the contents of /home onto the root partition, then overwrite all of /home with the contents of /usr and mount it as such, then moce the copied contents of home back onto the old /usr parition. It's quite logical and striaght forward really, but very easy to screw up if you're not sure what you'er doing, which may well be the case here.