Can you please give us your business requirement clearly? and in what scenario it will be using and the output
1) Do you want to edit/modify the path configured by author in path filed after selecting path one to path two?
i.e
path configured: /content/abc/def
path after edit / format: /content/abc/defpage
you don't have to provide another option to edit again the configured path. you can modify using Javascript or Sling Model to manipulate the path configured and send to output HTML Page.