Isn't it their way or the highway?
I don’t know enough about the UCC denominational structure to know whether it would tolerate a doctrinally-conservative congregation. I’ve seen liberal denominations in which lone-wolf conservative congregations have thrived—United Methodist, for example. And Congregational Churches are just that, so that the CCs in Pasadena (”Lake Avenue CC”) and Sierra Madre (SMCC) have been conservative for decades and are responsible for hundreds of thousands of converts.