“And what happens if they excommunicate you for believing in the Word of God?”
Nothing.
Schismatics and heretics have no authority to either modify church law, declare saints, ordain, nor bind and loose as in declaring one excommunicated.
Please do see http://novusordowatch.org/ for more on this.
So in other words, Protestants may have had a point when they challenged Catholic authority, because they are not, in fact, infallible?