Why change continuity when there's no reason for it, though? What does Babs gain by having been a cop? If anything she loses by it. Being a librarian feeds into her nerd characterization and gives her the skills she needs to be Oracle. Being a cop takes that away, and makes Batgirl redundant besides (if you don't change her characterization), or completely alters both Batgirl and Barbara (a cop steps outside the law as a vigilante for very different reasons than a librarian, which changes her entire perspective on crime and crimefighting, alters the way she would have behaved as Batgirl and how she'd behave now as Oracle, and makes her a Huntress1 or Manhunter4 clone instead of the exceptionally unique (because how rare is true uniqueness in comics) character she is now).
Okay, now I'm putting parentheticals inside other parentheticals. Clearly I need to go make dinner and not come back until I'm properly blood-sugared and coherent.