Your decree or how you think the judge will do things doesn't matter. It is idiotic on your part to argue the part of the issue that has already been communicated to the OP by her lawyer. First, you don't have the information that the lawyer has. Second, you aren't qualified to argue it and finally, that wasn't the question the OP asked.
I've been married a few months short of 15 years and I haven't changed my name with the MA Dept of Revenue yet. And it was the SSA that told me it didn't matter whether I changed my name with the Feds or the state first.
At the same time, I made sure that all the name changes had taken place with state agencies, Federal agencies and my employers before I filed any tax returns. I bet not even Indiana cares what order you do them in as long as it's all done before you file a tax return.
No I did not tell her to ignore her lawyer. I said that she should ask the judge about her name at the final hearing. That is what I said.
You can bow down to the lawyer. But the judge can do what the court decides. If OP were speaking about child support, alimony, division of property or custody, then maybe a new agreement would be necessary. But a name change? I don't think so.