Not so,
Here is how you would remove the nailed in closed 2x4 wall box installed before the drywall was placed.
I have developed a technique for removing existing closed in wall boxes that are nailed with two nails in the studs, without damaging the drywall. You first have to determine on which side the stud is located. With a jab saw, carefully cut the top and bottom corner away from the stud all the way to the back. Fold the side into the cavity of the box. Using a pair or heavy electician's pliers grab the top of the box at the loose end near the cut corner and rotate the end into the box. This releases the top nail from the box. Do the same for the bottom. Using a large screwdriver, bend the nail up or down away from the box. Carefully pull out the box with the electrician's pliers. After the box is out, take off the existing cables, and pull out and discard the nails.
The orange "old work" Carlon open box bracket sold for about $1.30 at Home Depot ot Lowes is ideal. I've been making these for over 10 years from the blue closed "old work" boxes for over 10 years, before the ready made ones became available. I just cut the backs off with a band saw. I still do this, since Carlon has revised the "old work" boxes to fit a regular rectangle, instead of the weird cut out pattern. They have not yet done this for the orange brackets, though. The nice thing about the new "rectangular cut out pattern" is that it fits almost perfectly into the space from a removed existing box.
In the case, where the hole was improperly cut in the wall for the box, I carry pieces of 4x6" 1/4 inch plywood, with a space on the long side cut out in the size of the "old work box." I slip this in behind the wall and glue it in with fast setting carpenter's glue.
The 2x4 inch of opening provides plenty of room to fish wires even through insulation.
That technique, however, requires a lot of experienced skill.