Is supplicating for one's parents with "O Allah, have mercy on them as they raised me when I was young, and forgive them as many times as You have created in the heavens, and as many times as You have created on the earth, and as many times as You have created in between, and as many times as You will create" considered an transgression in supplication?

It is better for a Muslim to supplicate to Allah with comprehensive and well-attested prayers found in revelation, and to avoid newly invented, elaborate supplications. The phrasing "(And forgive them [my parents] as many times as You have created in the heavens, and as many times as You have created on the earth, and as many times as You have created in between, and as many times as You are going to create)" should be avoided. Instead, one should use the well-attested forms, such as the supplication of Noah (peace be upon him): "My Lord, forgive me and my parents and whoever enters my house a believer, and [forgive] the believing men and believing women. And do not increase the wrongdoers except in destruction," and the supplication of Abraham (peace be upon him): "Our Lord, forgive me and my parents and the believers on the Day the account is established." The Permanent Committee has issued a fatwa (definition) stating that there is no basis for the phrase "I seek forgiveness from Allah as many times as He has created," and that it is better to abandon it because remembrance (dhikr) and seeking forgiveness are acts of worship that are not valid except through textual evidence. Scholars are of the opinion that adding numbers to acts of remembrance does not necessarily multiply their reward. The consideration is the number of times the remembrance is uttered. So, saying "Subhan Allah (Glorified be Allah) as many as His creations" means that Allah deserves glorification by this number, and it does not mean that whoever says it has glorified Him many times; rather, it is considered a single glorification.