Can a divorcing spouse make a new will before the divorce is finalized and have it be legal?

Yes. The effect of a subsequent divorce on a will is that the will is to be read as though the ex-spouse had predeceased the maker of the will. My advice would be to make a new will reflecting the change in circumstances, so as not to invite questions or challenges upon death.

A spouse can make out a will at anytime. If there are any defects as it may relate to a divorce, this is cured when the will is probated.