Okay, let's get a couple of things straight. First of all, to be in handcuffs, you do not have to be arrested. An officer may handcuff and "pat down" someone just for his safety (let's remember that a killing had just occured so handcuffing Zimmerman would have been warranted). You may be detained, a legal definition of taking away one's freedom just short of being arrested. Or, the police may have asked him to come to the station with them. A lot of police departments do NOT let people into their vehicles unless they've been searched for weapons AND they are handcuffed behind their backs (they only handcuff people in the front on cop shows).
A person may be read his Miranda rights at anytime. Usually, if you think or even don't know that the person has committed a crime, you read them their Miranda rights. Arrest or charging someone with a crime has nothing to do with Miranda rights. You can be arrested all day without being read the Miranda warning so long as they don't ask you any questions regarding the alleged offence.
An officer affects an arrest when they say to the person, "You are under arrest." Or something of that nature. There is no legal requirement for the officer to explain to the person the specific charge, although its good policy to do so. Charges are specified in the arraignment. You can be arrested, handcuffed and sent to jail without anyone ever saying "boo" to you. And no, you do have a legal obligation, once arrested to provide your CORRECT identity.
The only way to tell if Zimmerman was arrested is to find out if he was arraigned. Anyone who is arrested has a right (it's in the constitution) to have their day in court. So if a cop arrests you, he can't legally simply "unarrest" you (although I know of thousands of times thats happened - I've even done it). He (legally) has to give you your day in court and you have the right to demand it. By advising you that you are under arrest, the officer has taken away your freedom. If he simply "unarrests" you then he has committed false imprisonment. NOT a good idea.
Sniper Zimmerman was not arrested. To know this you would have to know the Florida Statute's were for making an arrest. I just found out this yesterday.
A letter from the city manager of Sanford
Why was George Zimmerman not arrested the night of the shooting?
When the Sanford Police Department arrived at the scene of the incident, Mr.
Zimmerman provided a statement claiming he acted in self defense which at the time
was supported by physical evidence and testimony. By Florida Statute, law
enforcement was PROHIBITED from making an arrest based on the facts and
circumstances they had at the time. Additionally, when any police officer makes an
arrest for any reason, the officer MUST swear and affirm that he/she is making the
arrest in good faith and with probable cause. If the arrest is done maliciously and in
bad faith, the officer and the City may be held liable.
According to Florida Statute 776.032 :
776.032 Immunity from criminal prosecution and civil action for justifiable use
of force.—
(1) A person who uses force as permitted in s. 776.012, s. 776.013, or s. 776.031 is
justified in using such force and is immune from criminal prosecution and civil action
for the use of such force, unless the person against whom force was used is a law
enforcement officer, as defined in s. 943.10(14), who was acting in the performance
of his or her official duties and the officer identified himself or herself in accordance
with any applicable law or the person using force knew or reasonably should have
known that the person was a law enforcement officer. As used in this subsection, the
term “criminal prosecution” includes arresting, detaining in custody, and charging or
prosecuting the defendant.
(2) A law enforcement agency may use standard procedures for investigating the
use of force as described in subsection (1), but the agency may not arrest the
person for using force unless it determines that there is probable cause that the
force that was used was unlawful.
http://www.sanfordfl.gov/investigation/docs/Zimmerman_Martin_shooting.pdf