What happens when an expert goes from "testifying" to "consulting?

It’s fairly common for a BV expert to sign on to a legal case in a “consulting” capacity. Not only might this reduce costs during the preliminary phases of litigation, it shields communications between the expert and attorney—and any preliminary reports or work papers—from disclosure and discovery, absent “exceptional circumstances” (the standard under the federal rules). Should the case heat up and head for trial, the attorney can “promote” the expert to a testifying expert, subjecting his/her opinion to the applicable rules, including the recent amendments in federal court and Tax Court that now protect most draft reports and communications from discovery.

But under what circumstances may an attorney “demote” an expert from testifying to consulting?  The concern: An attorney may seek to de-designate its expert to prevent the other side from discovering a “bad” opinion (read: unfavorable to the client’s position). At least one court has held, according to a new article from the Gibbons law firm, that once an expert is designated as testifying, “he can be deposed and possibly called at trial,” particularly when that expert has already issued a report. By contrast, another cited case followed the majority approach that requires "exceptional circumstances" to depose a de-designated expert.

Landing in jail, and other ‘good cause’ for an expert’s substitution. The Gibbons article also discusses the “expert pivot” in litigation, or the circumstances under which a court will allow a party to change its experts in midstream. In one case, the expert’s incarceration amounted to the necessary “good cause,” but in another, the expert’s alleged “medical condition” was not enough to sway the court from believing “gamesmanship” was the real reason behind the switch.