[Tkinter] Defining a self made module's function to interact with the main .py variables?

[Gribouillis]

before I make changes and flow with them and finally nothing will work

That's a reason why version control systems exist. I hope you're already using one such as git, to keep tracks of previous versions of your code and potentially restore them.

can u please elaborate on the file=file definition?

It is only the default argument syntax in functions signatures in python

>>> spam = "Hello"
>>> 
>>> def func(x=spam):
...     print(x)
... 
>>> func(x='eggs')
eggs
>>> func()
Hello