I'm using the icathian rain , and the opponent has 1 Predator on their base In this way, can I stop after giving only 2 damage to the deflect unit? Is it possible to pause the gameplay midway because the deflection feels overwhelming when making a judgment?

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Short answer: Deflect never caps how much damage you deal — it's a cost, so "stopping at 2" depends entirely on what's dealing the damage, not on the Deflect unit. If you're dealing a fixed amount to a chosen target (a spell like Falling Star or a 2-damage effect), you deal exactly what the card says; you can't reduce it to 2. Deflect just adds mandatory Power when you choose that permanent (Rule 809.1.c), and it's paid even if the damage ends up prevented or the ability later fizzles (FAQ #2811). If you have no other targets you will have to deal all the instances to the predator with deflect as you need to be able to execute the spell fully. However, you can not play the spell and this will prevent you from paying the extra deflect, even "mid cast". On finalization you realize you don't want to play this, you absolutely can as long as it has not become completely finalized. You will have revealed a card, but you won't lose your runes in the process. Where "stopping at 2" does work is with Repeat: you can simply decline to pay the Repeat cost and let the spell execute only once, so the Deflect unit takes just the base 2 damage — but the Deflect cost is mandatory per time you choose it, so if you do pay to repeat and target that unit again, you owe Deflect a second time (FAQ #9293).