transposition (n)
switch (n)
substitution (n)
replacement (n)
permutation (n)

Definition: an event in which one thing is substituted for another
Example: the replacement of lost blood by a transfusion of donor blood.

change (n)

Definition: the action of changing something
Example: the change of government had no impact on the economy. his change on abortion cost him the election.

alteration (n)
change (n)
modification (n)

Definition: an event that occurs when something passes from one state or phase to another
Example: the change was intended to increase sales. this storm is certainly a change for the worse. the neighborhood had undergone few modifications since his last visit years ago.