Under the circumstances of this universe, the Japanese might consider using gas against Corregidor (or other points - once the genie is out of the bottle). Even in the IJA's operating mindset, would that open Pandora's box for reprisal's by the Allies?
Just think, one isolated island is holding up timetables all across the ' co-prosperity sphere' something needs to be done, fast.
Downside for the IJA was almost 90% of all gas warfare gear and stocks was in China, Pacific theater troops were the worst equipped to deliver, or even defend against gas.