Even happens when i use command to re-reseach all related techs.

force.reset_technology_effects() is the culprit. Is it possible to enhance biters by buff them rather than decrease torret damage?

That definitely is a troublesome function and a lot of mods rely on it not being called. I'll see if I can keep track of where modifiers should be and modify them appropriately instead of relying on reset_technology_effects()

I've searched around Factorio API but seems like there's no way to modify the attribute of entity in game. A trival solution might be... generate as much tier of bugs as user want through config?

Rampant use some nice template to generate its large biter prototype library and it offers 10 tiers of biters each kind. But attributes are hardcoded in prototype luas. I'm not sure if factorio can store 1000 tier of biters in memory without crash... but that might be so fun ;)

I updated the mod with a method that doesn't rely on reset_technology_effects(). This may cause a problem if any other mod changes turret damage by means other than technology.