When someone has skin reduction surgery, can that be used for skin grafts for others?

No: Skin can be transplanted in same individual but not in others.

Testing too costly.: In the vast majority of instances the tissues are discarded as medical waste and incinerated. On occasion the tissues may be used in the same individual as a pedicled flap as seen in the tram flap procedure for breast reconstruction. The component tissues can be used as a skin graft or the fat can be harvested and used for breast or buttock augmentation only in same or identical twin