Is it perfectly acceptable to take off a fitting and solder a coupling to it, as opposed to going back and soldering to virgin pipe?
Nothing wrong, except that it is more difficult to re-use a fitting or resolder to a length of pipe.
The solder residue from the previous time might be too bulky to fit the parts together.
For one reason or another, the joint made with re-used parts often develops oxidation inside during reheating and the solder doesn't seal the joint properly and it leaks.
The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded.