Well I suspect the prosecutor will argue that there was some sort of error and that the correct date is the one that he changed it to. If you do not have an attorney hire one. If you have an attorney listen to that attorneys advice. Certainly this raises questions of fact but the court will not dismiss the case unless there is something more.
The question is what was the actual date of the crime? That is what matters.
I see nothing improper or unethical about what the prosecutor did, although the drafting of the original charge may have been careless. When you established an alibi for the date charged the prosecutor very properly checked it out. If the investigation had confirmed your alibi the state would have had to consider dismissing the charge. Instead the investigation apparently disclosed that they had charged the wrong date, and they fixed that mistake. Of course, if you can show that the police have now faked the date of the crime and charged a false date in order to evade your alibi, you have a very good chance of being found not guilty.
The prosecutor can change the indictment at any time pror to trial. You may be able to use the change to cast reasonable doubt on their case, unless there is some relaible evidence that the prosecutor's new date is reliable.
This question is not so easy to answer. It is unconstitutional for the prosecution to manufacture evidence against you. I don't know if that happend or not. Even if it did happen, you might not be able to prove it did.
There are ways to attack this, how to deal with this situation is something you need to discuss with your lawyer if you have one. If you do not, I would be happy to speak with you about it. Call me at 803-575-0384.