Like a BFR?
A man’s reach should exceed his grasp...
A BFR is only the rocket. You need to have some sort of human-rated maneuverable craft attached to the BFR which is capable of carrying tons of cargo needed to make the changes and which cargo is easily accessible to the astronauts who will install it. Picture the Space Shuttle which once rebuilt the Hubble, now defunct. There is no such craft available presently or in design for the future.
Can’t be done now.