Should I replace Experaction with lighting breath?

no

There really is no point in doing that. Waste of time, effort, resources, and in some cases you're downgrading.

He's already a tank. Don't waste your resources.

Lightning Breath+ over Expiration
Pros: +5 hp, potential +3 spd/+4 def/+4 res
Cons: -4 atk (unless you get atk upgrade, which wouldn't make sense) and +1 special charge
Honestly, I feel the reduced charge and extra atk is worth more than additional defenses.

No nope never no es bueno please never.

Like everyone here said, it's completely unnecessary. Expiration has the same exact effect as a refined Lightning Breath+. The only benefit you'd get from switching to LB+ is a few more points in BST, which seems like a huge waste of resources for a few more stat points.

No, no, no.