Yes, just used the config
method:
label = Label(root,text="this is text!")
label.pack()
label.config(text="that was text!")
Another way to do this would be to set the textvariable
attribute of the label.
textvar = StringVar()
textvar.set("this is text!")
label = Label(root,textvariable=textvar)
label.pack()
textvar.set("that was text!")
In this case the label
instance will automatically update its text when the textvar
instance is updated.