The simplest implementation is the one that is identical to all others. If the standard adopted stipulates that HCPCS codes will be used to describe procedures, then the health plan must abide by the instructions for the use of HCPCS codes. A health plan could refuse a code that was not applied in accordance with the HIPAA national standard coding instructions, but could not refuse a code properly applied for reasons of policy unrelated to the standard.
For example, if the standard stipulates that the most specific code available must be used, then a health plan would be right to refuse a code that does not meet that criterion. The health plan would need to work with the committee(s) governing the particular coding scheme to have codes adopted that meet its needs.