Seems to me thought should be made to just build new replacement airframes
Unless they are technologically obsolete..: building new airframes certainly will be cheaper than designing and building an entirely new plane
The majority of the B-52 fuselage is unpressurized. The basic airframe sees very little stress compared to commercial airliners.
The wings are the component that sees the stress because they flex about 15 feet from takeoff to cruise. They flex even more during maneuvering.
Because of that, they have been reskinned, some more than once.
I agree with your statement that building brand new B52’s should be cheaper.
This brings to memory an article I read on the A1E Skyraider I think was built by Douglas. The aircraft could carry such a huge payload and loiter for so long that the USAF wanted them back in production. The problem was the cost was so atrocious it was deemed not worth it.
Boeing could do the same here. After all, the maid idea of the military industrial complex is to make money.