Progressive Severity of State Effects

Hi, I am trying to implement a skill/state effect that causes a "Chilled" effect that will progress into a "Frozen" state.
It goes like this: "Chilled" (71) -> "Frigid" (72) -> "Frozen" (73)

So basically, if a battler uses a skill that causes the "Chilled" state onto a target, the target would have the "Chilled" state applied.
Next turn, the battler uses the same skill again on the same target, the target would have the "Frigid" state applied instead.
Finally, if the battler uses the same skill yet again and the target is already "Frigid", the target would be"Frozen" instead of "Chilled".

I know I'll at least have to use code involving...

if (target.isStateAffected(71)) {
target.removeState(71);
target.addState(72);
}

Not sure if I should be using <Custom Confirm Effect> or perhaps <Custom Apply Effect> or something else?

You don't even need a plugin to do that, just put it in the damage formula. Use "b" instead of "target" and you're done.
Also you should tell what plugin you're using because those tags don't exist by default in MV.

Right sorry, I'm of course using Yanfly's Buffs States Core and most of his other plugins really.

Thx for the tip. I was looking at this all wrong trying to put the code in the state's text box instead of putting in the skill's text box.

I still have a lingering question though: Are states applied before or after damage evaluation?

<Confirm Effect> will trigger upon a successful hit, and skip if missed/evaded. The state should be applied at this time.
If you want to apply the state BEFORE damage calculation, you should use his Skill Core plugin and make used of <Before Eval> lunatic tag.