Permissions to overwrite a file - Without allowing them to add new files

Hello,

I have a set of users which I need to give permissions to simply overwrite an exisiting file, without the ability to add new files.  They have a newsletter, and they need to overwrite this existing file 

For the enclosing folder I'm giving them Read, Change and Publish rights.

For the file itself I'm giving them Read, Create, Change and Publish rights.   

In theory, this should allow them to drag-drop a file with an existing name and overwrite it, which is what I need to do. 

Any advice?