Yes, COMMUTATION is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, M 3, M 3, U 1, T 1, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

COMMUTATION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the travel of a commuter
a warrant substituting a lesser punishment for a greater one
(law) the reduction in severity of a punishment imposed by law
the act of putting one thing or person in the place of another: "he sent Smith in for Jones but the substitution came too late to help"

Also: re-sentencing.