When the askyesno pops up, there are 2 buttons: Yes and No, but I want to customize these buttons to "OK" and "Cancel", for example.

Add the Askyesno module import.

Snippet:

def confirm_choice():
    response = askyesno("Are you sure you want to choose this text file?")
    if response:
        print("User chose Yes")
    else:
        print("User chose No")