All praise is due to Allah, and peace and blessings be upon the Messenger of Allah.
It is permissible to describe Allah as the Planner and Director of all affairs (Al-Mudabbir) because the Qur'an affirms that He manages and directs the affairs of creation. Allah says:
"He arranges every matter."
(Qur'an 10:3)
And He says:
"He arranges every matter from the heaven to the earth."
(Qur'an 32:5)
Allah is the Creator, the Sovereign, and the One who directs all affairs of His creation. There is no disagreement regarding the correctness of this description.
The Names of Allah are tawqifiyyah, meaning they can only be affirmed through authentic evidence from the Qur'an or the authentic Sunnah. They cannot be established merely through linguistic derivation or rational deduction.
As far as is known, there is no explicit, authentic, and universally accepted text stating that Al-Mudabbir is one of Allah's Beautiful Names.
However, some scholars considered it one of Allah's Names for one of two reasons:
For this reason, scholars have differed over whether Al-Mudabbir should be counted among Allah's Beautiful Names.
The safer approach is to say:
Allah is the Director of all affairs and the Manager of creation, because this description is explicitly established in the Qur'an.
As for definitively affirming Al-Mudabbir as one of Allah's Beautiful Names based on an explicit authentic text, there is no scholarly consensus supporting this.
Nevertheless, whoever regards it as one of Allah's Names by following scholars who accepted the relevant narrations or derived it from the Qur'anic texts should not be criticized, as this is a matter of scholarly reasoning (ijtihad).
Allah's Names are not limited to ninety-nine. Rather, the meaning of the hadith is that Allah has ninety-nine Names such that whoever learns, understands, and acts upon them will enter Paradise. It does not mean that Allah has no Names beyond these.
The Prophet's supplication also indicates that Allah possesses Names known only to Him in the unseen.
Describing Allah as the Director of all affairs (Al-Mudabbir) is correct and firmly established, because He directs the affairs of the heavens, the earth, and all creation. However, considering Al-Mudabbir to be an independent Name among Allah's Beautiful Names is a matter over which scholars have differed. Some affirmed it by deduction or based on certain narrations, while no explicit authentic text universally establishing it has been proven. Therefore, the issue remains one of scholarly judgment.
And Allah knows best.