Allaah has said (interpretation of the meaning):
Unto Allaah belong the beautiful names. Pray to (and ask of) Him using them.
As part of the prayer to Allaah using His names, we call on him by saying, O Merciful, have mercy on me; O Forgiver, forgive my sins; O Provider, provide for me, etc.
However, to read a specific verse a certain number of times (whether 99 times or whatever else) without any valid documented evidence is a bidaah (an unacceptable act of innovation in religious practices) that is not permissible. Such acts invent a way to worship Allaah which was not revealed or taught by Islam. The Prophet (peace be upon him) said:
Whoever innovates in our religion a new act (of worship) then his act is rejected" (Sahih al-Bukhari, Fath al-Baari No. 2697.)
The best guidance is that of the Prophet . There is no allowance for innovation in the religion of Allaah. Is it possible for us to discover new things in our religion that the Prophet didnt know? Indeed, it is incumbent upon us to read the Koran in the way the Prophet read it, we need to pray in the way he prayed, and glorify Allaahs name in the way the Prophet has been validly reported to have done.
Only Allaah is the one who provides success, and He is the one who guides to the right path.