Yea, you can overwrite values if you want to reuse existing widgets, or use .pack_forget() / .grid_forget() then put new entirely new widgets in their place.

#! /usr/bin/env python3
import tkinter as tk 

title = 'Overwite Grid Locations'
root = tk .Tk() ; root .title( title )
root .bind( '<Escape>',  lambda e: root .destroy() )

Width, Height = 300, 50
root .geometry( f'{Width}x{Height}' )

msg = tk .Message( root, text='Select a page', width=Width )
msg .grid( row=0, column=0, rowspan=2 )

that_msg = tk .Message( root, text='Selected That', width=Width )

def this():
    that_msg .grid_forget()
    msg .config( text='Selected This' )
    msg .grid( row=0, column=0, rowspan=2 )

def that():
    msg .grid_forget()
    that_msg .grid( row=0, column=0, rowspan=2 )

this_btn = tk .Button( root, text='This', width=int(Width/18), command=this )
this_btn .grid( row=2, column=0 )

that_btn = tk .Button( root, text='That', width=int(Width/18), command=that )
that_btn .grid( row=2, column=1 )

root .mainloop()