IAs I understood it, Mr. Arnold's sole qualification for serving as Paramount archivist from that era was the fact that he was already employed as Mr. Roddenberry's manservant.
Incorrect.
Richard Arnold met the Roddenberrys at the first Bjo Trimble ST conventions when he was a teenager. He also ran the Official Grace Lee Whitney Fan Club for a time, IIRC. As a young adult he'd moved to LA and got
volunteer work, for many years, as a studio guide for Paramount, and helping Majel with Lincoln Enterprises. He impressed GR with his photographic memory and, when ST IV did so well at the box office, GR was finally able to get him a weekly salary as "ST Archivist" at Paramount.
Gene's "manservant", as you called him, was his limo driver and personal assistant,
Ernie Over. He wasn't employed by Paramount, but paid from GR's payroll. He was GR's fulltime carer after GR's two debilitating strokes. After GR died, Ernie continued as Majel's personal assistant and driver for at least a year.
Roddenberry sought to monkeywrench certain aspects of TOS-TAS-TNG continuity because some of the ideas (double-digit warp factors, etc.) were not "his" and were therefore declared no longer "Star Trek fact".
No. In 1989, Filmation Studios was being dissolved - and ownership of their back catalog of cartoons and TV shows was
in legal flux. It was easier to declare TAS off-limits to the licensees of ST tie-ins at the time. The memo issued by the then-ST Office was not enforced after GR's death in 1991.