Based on the Omega Leader-HLC precedent: A ship that attacks with HLC must change its crits into hits. Locked by and attacking Omega Leader it is prevented from doing so and has to keep the crits.
Now M9-G8 says "You may chose one attack die, the ship must reroll it", which is the same wording as HLC and refers to the attacking ship. This is mostly important for Snapshot shenanigans that won't work with M9-G8. I've seen a few people talk about this, but I don't believe, based on whats already in the game, that its possible.
I'd be happy to be corrected, but I am afraid the case is quite clear.