The element changes only when the bonus damage from it is triggered, including during creature attacks. If you use the "Rain" spell on fire, water, or earth, their elements will not change. In attack, instead of cold, it's much better to use tactics, because otherwise, the entire Orc army will be able to reach you from the first turn, and you won't have anything to fight with. You should only focus on attacking Cyclops if they have a tactic that involves a large number of stacks of leaders, followed by reinforcements; otherwise, there are more dangerous stacks. In general, Erin works very well with the slowing cold effect.