No. Any given figure can't have more than one instance of a specific condition, positive or negative; this is explained in the section of the rules on conditions.
Piggybacking off this, what stage does the extra damage from poison belong under when an attack is performed? There's attacker bonuses, then modifier deck, and then defensive bonuses. I'd assume it's a negative condition under defensive bonuses, but I'm not sure. Or is it just a flat 1 damage regardless of how much damage the attack does otherwise?
Poison happens before the attack modifiers (rulebook page 20, 1st bullet)
Some of these things are hard to track down. It also doesn't help that "modifier" is reused throughout the book - sometimes for Attack Modifier Cards and for other stuff like poison.
It is why I created this: