No vi (Visual Editor) won't create a new file when invoked upon an existing file. It will simply open that file and you can edit and make changes upon that file.
It *might* create a backup file, in this case, "interfaces~", while the newly changed original, "interfaces" will contain the edits (changes) you made.
If you're not familar with *vi* or *vim*, then perhaps substituting out a different editor like *nano* would be best for you to begin with.
I hope that helps