Re the Darby issue. First, I am NOT a lawyer. So, I'm not representing that what I'm saying is legal advice. However, I am all but certain that unless the original terms included at least a clause saying that the terms can be amended, then the original terms are binding for the full length of the CD term. It otherwise would constitute breach of contract -- as the CD is a contract. Any first year law student should be able to tell you all about this.
Now, even if there were a clause providing for amending the terms, I do not presume they can do so to any and all parts of the terms, or that they can do so to any parts of the terms unilaterally. But that would be a trickier legal question.
I note, many lawyers operate under a tactic that basically amounts to "if you can get away with it, then its legal." So, change the terms in midcontract and see if you get away with it.
On the other hand, there also might be ability for the FDIC or other government agency to override the CD terms and force Darby to take such action. I have no idea about that. But, is Darby under any financial stress; has the FDIC given any warnings to Darby?
Lastly, surely there must be some government agency you can file a complaint with. Maybe the FDIC? Maybe your state banking department? If no one else, your state attorney general or the federal prosecutors office? Seriously, file one. At least file with the Better Business Bureau.