How to rename a CSV file by adding MODIFIED in the filename?

[Larz60+]

Python_user writes:
As addition, why isn't root = Tk() used in this code?
In the video below at 03:45 the guy says this should be used always in Tkinter...?

The 'guy' is only partially correct, There are some tkinter modules that can be run as stand alone.
The filedialog and messagebox are examples of this.
Technically, perhaps a root window should be created, but these classes function without.
Don't forget, tkinter is just a wrapper around tcl/tk.

Could you provide some explanation behind the lines of code as comments?

perhaps I can get to documenting the entire code.
I wrote it in 10 minutes, and haden't planned on documenting, I have my regular work to do, as well as answering so many questions (as a volunteer) on the forum.
Always glad to answer specific questions.