Does the wording "رسولاً" (messenger) and "رسول" (messenger) in the two verses "فأتياه فقولا إنا رسولا رب العالمين" (Go to them and say: 'Indeed, we are messengers of the Lord of the worlds') and "فقولا إنا رسول رب العالمين" (So say: 'Indeed, we are a messenger of the Lord of the worlds') contradict the understood meaning in creed that Aaron was a prophet and not a messenger, or is the meaning in them from a linguistic perspective?

Aaron was a prophet and a messenger. Allah Almighty sent him with his brother Moses to Pharaoh. Evidence for his messengership is Allah Almighty's statement, on the tongue of Moses: ("And appoint for me a minister from my family - Aaron, my brother. Strengthen my back with him and make him share my task"), and Allah Almighty's statement: ("So go to Pharaoh and say: 'Indeed, we are messengers of the Lord of the worlds'"), and Allah Almighty's statement: ("Indeed, we are messengers of your Lord").