Although you are with interim management and without HIMS leadership, your facility should still have a compliance officer. Along with a compliance program, I'd imagine there'd be hotline to support the reporting of potential compliance violations.
Since HIPAA does mandate code sets be kept current as part of the Uniform Data Set, this is a compliance issue. If you have a hotline or a compliance officer at hand, present the issue in a professional manner to this individual, who should carry enough weight and influence in the organization to effect change. The other option is to anonymously report this to compliance, in helping your hospital get with the program.
Other than that, and as already mentioned, just wait for payments, denials and host of other back-end work pile up and see if that gets leaderships' attentions. It's so unfortunate to see your management company ignoring the needs of your facility, especially at a time when most hospitals need to recoup as much money as possible to stay competitive.