Wrong.
1) Once you are arrested, the IO conducts an investigation. If that investigation shows a prima facie case of an offence being committed. He would have to prefer the charge. He cannot drop the charge, down grade the charge or come out with his own charge etc. If there are extenuating grounds not to charge him such as school student, existence of mitigating factors etc, he can make the recommendation to his Sr Officer for support only. If the Sr Officer agrees, it will have to go to AG for DPP to agree with the recommendation and make the decision.
2) If the investigation shows that charge that he was originally arrested does not fit the crime, the IO can then charge for the crime that is disclosed.
3) If the investigation does not disclose a crime, the case is classified as NOD (No offence Disclosed) and the accused is released by the IO. For points 2 and 3, no need to go to AG.
4) If the DPP agrees to a lesser charge, the case proceeds with the lesser charge. If the DPP agrees to a warning, the warning must be administered by the Rank of ASP and above or to a designated person assigned by the ASP.
Note: Except for the Attorney General and his designated staff, no charge can be reduced or withdrawn. No Police Officer, or enforcement officer including those in CPIB, Customs, immigration can reduce or withdraw a charge. Even the Commissioner cannot do anything.
The operating principle of control is called "Separation of Duties" to avoid another principle -"conflict of interest". The primary reason is to avoid corruption. The DPP who makes the decison has no clue if the accused is a sexy women with a mini skirt or a fat lady that looks like the back of a bus.
Members of the public arrested by the Police and have been warned or have their charges reduced are not shown the Investigation Paper which go to the AG Chambers. The same with police officers doing all other duties such as patrol etc. They are not aware what has taken place.
Why bother to have an AG, chambers full of prosecutors when the Police can do all these things in the cheap.
This is yet another example where you do not understand how control and organisational principles apply.
Here is a simple case for example.
A good student aged 19 in a Uni gets arrested for shoplifting. She is brought to the station where she will be charged in station charge book for shoplifting. She cooperates with the police and they realise that she is a student. As she is cooperated, they will refer to AG for a warning in order not to destroy her future. In the meantime she is released on bail for the shoplifting charge. If DPP in AG Chambers agrees. The file is sent back and she will be called a few days later for a warning to be administered. Note: the decision was made by DPP and not the Police.
Same student, same situation but she is kwailan and disputes the allegation. Police hands are tied. They will charge her in court. The Police can't make any recommendation in this instance.
Note: This example should not tempt anyone to plead guilty for serious cases. In such cases, it best not to implicate yourself and then seek legal advice. Be nice to the Police IO, provide all details except those that might implicate you.
You must be clean as a whistle good boy never been arrested by police before. There're two stages the charge passes through, station charge and court charge. The police hold you at lockup or out on bail pending investigation on station charge. Any bargaining could and should be done with IO then. He can even drop the charge. Once he charged you in court and you claimed trial, it's harder but not impossible as DPP takes over.
There's not many bargaining chips you're likely to have with DPP except through the skills of your lawyer, since DPP isn't interested in information and investigation, he just takes over the files from IO. At investigation stage, you're more likely to have bargaining chips as with information and confession.