Quoted from Noah's Chapter 5 Story Quest "Righting the Wrong": Yes! I still have the power of the Moon that the imposter injected in me. Even if it mutated just like my power of Darkness, the fundamental property of regeneration should still remain.
Noah's main story path is Liberator, so since his moon power is mutated in that path as well, his moon power wasn't mutated by Clamor's Celestial Magic.
Edit: It's also a mention that the Order injected the moon power into him.
The order injected a liquid into him... which mutated his power of moon also. There is no explicit statement that says its SUN POWER.
Stellar Caster discovered that the moon power mutated because of sun power. I already explained why it can't be the celestial magic Clamor taught him.
Edit: Also, he used that knowledge to manipulate time, confirming it's the same time-altering ability causing his loops.
Noah Chapter 3 Story Quest: Dark Side states that Noah was in bedrest since he received the power of the moon, and we know he was bedridden long before the El Explosion, meaning the liquid he was injected with after the El Explosion was intended to be a stabilizing agent, not the mutated power itself.
Henir = injected unknown liquid. Noah had low affinity for moon but still has it.
Story quest= reveal that henir injected a mutated version of power of moon infused with power of sun.
Your own quote... "I still have the power of the Moon that the imposter injected in me."
meaning that the liquid injected into him is not the power of the sun
Noah Chapter 3 Story Quest: Dark Side
Noah: The El Master receives the purest elemental El energy from the High Priest during their nomination. I think the imposter tried to inject me with the power of the Moon after he received it.
Clamor: Why would he... Never mind that. Is it alright for just anyone to receive the power of the Moon?
Noah: Well... At the very least, it wasn't for me, since I had to be on bedrest after that. My body can't really tolerate the power of the Moon. I could barely hold it in...
Clamor: Are you still ill? Noah...!
Noah: I'm fine now.
Noah: ... I told you, they were conducting a final experiment. I don't exactly know what it is...
Noah: But after that pill they forced me to swallow, the power of the moon I barely held, and even the power of Darkness I already had... mutated.
... Huh. They changed it to a pill... How did I not notice that?
Noah stating he still had the power of the moon that was injected to him didn't mean that the power was still in the exact same state as when it was injected, it just means that the power never left him.
Noah get power of Moon = bed ridden
Henir dude gives a pill before the explosion = power mutated but noah retain white hair. At this point the pill should be the moon power infused with sun.
El explosion = other henir dude give unknown liquid which cause hair change.
actually thinking about it, im starting to think the henir guy that gave noah the unknown liquid was actually misty. She fake poison noah, changing his hair to black to so that the other members wont realize he is a ebalon and brought him to the altar. Meaning the liquid is not actually the mutated power.
The imposter got the power of the moon and injected it into Noah, leaving the latter bedridden simply by having it. Not using it, simply having it. Noah is forced to take a pill, which mutated his power of the moon. Noah still has the power of the moon mutated by the pill, but having it no longer makes him ill. Noah mentions the pill in the context of the final experiment.
All of this leads to me believing that the pill itself was the final experiment. And since it was the pill that mutated his power of the moon, it clearly had the power of the sun that Stellar Caster realized mutated his moon power.
Hmm, i was under the pretense that the unknown liquid injected into him was the mutation.
At this point im not even sure if the black hair was caused by the sun power