If one TLT Y-wing has M9-G8 and target locks a TLT Y-wing with the BTL-A4 title. The titled Y-wing is taking 3 attack roles but only declaring 2 attacks. Would I get to reroll one die per attack roll or 1 die per declaration of attack. In essence, if I reroll the first TLT attack, do I get a reroll on the second?

You get the reroll on all three attacks. "When attacking" abilities trigger on both rolls of TLT, because TLT makes two attacks. It's the same with stuff like Predator or Marksmanship.

You get the reroll on all three attacks. "When attacking" abilities trigger on both rolls of TLT, because TLT makes two attacks. It's the same with stuff like Predator or Marksmanship.

Yes. Specifically, M9-G8's rerolls happen during "Attacker Modifies Attack Dice" (3.ii on the flowchart), which is one of the steps that happens twice during a Perform This Attack Twice attack.