You should write the congregation' BOE and tell them you do not wish to continue as a member of that specific congregation.
In the same letter you should threaten to take legal action against the elders if they say anything to mar your reputation with your former congregation associates.
If you do this and they decide to DF you anyway and announce it, I highly doubt you would be successful in a lawsuit, and I am unaware of anyone who has been. Some bodies of elders, anecdotally, have decided not to make an announcement out of fear of personal liability and legal costs, but the chances of an actual successful lawsuit are slim to none.
The simplicity of their announcements is legally airtight. They have the right to discipline members by expelling them, and if you choose not to be a member they can't discipline you further, but merely accurately announce you are no longer a member. The distinction you are trying to make between withdrawing from the local cong vs. withdrawing from the religion is not going to do anything meaningful.