Local governments can make local decisions. This is the right move.
Only if the decisions don't violate state and federal law.
The state establishes school boards. It mandates that they shall produce a science curriculum. If the school board fails to do this, is members are subject to, among other things, impeachment and removal from office for high crimes.
Since the stickers amount to lying by omission (saying that biology is a theory and should be taken with a grain of salt, but not saying that for the rest of science), the school board is in violation of the law.