Prosecutors routinely overcharge for that very purpose - to allow the jury a “menu of choices” for their verdict. (2nd degree murder is the maximum that the jury can choose now.) The prosecutor has an ethical responsibility not to charge what she can’t prove. So she believes she can prove 2nd degree murder beyond a reasonable doubt. If/when Zimmerman asserts an affirmative defense under the Stand Your Ground law, the prosecution will fight it.
IIRC in the Casey Anthony case they had to prove first degree .....No other choices for the jury. All or nothing.
Remember several discussions about Florida law must state lesser degrees to convict of lesser degrees. You may want to check that.