Yes, ARROGATING is a Scrabble word!

Letter values in Scrabble US: A 1, R 1, R 1, O 1, G 2, A 1, T 1, I 1, N 1, G 2.

Is it a valid word?

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

demand as being one's due or property; assert one's right or title to
make undue claims to having
seize and take control without authority and possibly with force; take as one's right or possession

Also: lay claim, take over.