Thank you for the post.
I have responded to your post about global fields here:
Perhaps, you could clarify further what specific changes you wish to make to the hosted file? What changes are you unable to perform from the client side?
Many changes can be made live to a hosted file, such as layout creation or modification; however, if the file is in production, then best practice would be to work off a copy of the layout and switch out the layout after production ends for the day.