I want to outsource this task to a freelancer over the Internet. I don't have experience with outsourcing and don't know how to incorporate an outsider to the project. I mean I'd like to avoid other people to access the back-end source if I can. The only code that i want to be changed runs on the client side.
Is this doable? I thought I can just give the URL to the designer and require them to use "Augmented Browsing" tools, like Greasemonkey or Tampermonkey to work on the UI. Is this something Web designers are accustomed to or willing to do? Or are there any better options to accomplish this?