Yes this would change his place from where it is now. 3 weight class UFC champ ... not sure he'd be the GOAT without some defenses / more wins ... but it would move him in to conversations of some of the best all-time fighters and careers.
That said, if he went to 170 and fought Usman, he'd be like <3% or something to win the fight. I'd be very happy to lay the 4:1 or whatever the odds would be because Conor nut-huggers bet him getting 3:1 or w/e thinking he has a shot. In other words, he basically doesn't have a chance. Usman would murder him. He might not even wrestle him to just knock him out with jabs.