Like have 4 members in the party but only 2 of them out at a time? I don't see the point.

Anyways, the variable
MAX_PARTY is used to create caterpillar sizes, I think. Don't quote me on that

BlizzABS::Config::MAX_PARTY = number
Edit: Doing this worked for me.
BlizzABS::Config::MAX_PARTY = new_size
$BlizzABS.init_caterpillar
$scene.spriteset = Spriteset_Map.new