Alterations are modifiers that allow a player to alter gameplay features of turrets while keeping them within the overall game's balance.
For example, an alteration can weaken one characteristic in favor of strengthening another one.
For detailed information, check this article: http://en.tankiwiki.com/Alterations
i have m2 fire and i want to buy it's alteration ... .... but will the alteration stay when i buy m3 fire??
Yes, it will stay.
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