New file lockout

It would be handy to have a button which, when pressed/ticked, prevents new files from being inserted into a directory, but always allows current files to be overwritten. I guess it reverses the current system of checking for overwriting but allowing new files.

The reason for wanting it is so that when doing web pages development, it prevents accidentally ftping a file into the wrong location, because you always want to overwrite the old file with the new version, but you don't want to put it in a new place.