I understand this answer, it's just that it would be much easier to highlight a group of, say 50 individuals and make a new file from them, rather than having to import all 600 under a new name and then deleting the 550 you don't want.
In addition to this, it is virtually IMPOSSIBLE to delete people in this way because as soon as you try and delete someone who has connections with two families (through marraige for example) you can't do it as the system complains you would be spliting the tree into two sections. WHICH IS EXACTLY WHAT I WANT TO DO !