I am only vaguely familiar with references to certified coders being employed for the sole purpose of supporting compliance--I know this was mentioned years ago in relation to hospital compliance plans. However, if you read most job descriptions for physician coders, it requires them to make changes.
Internal policy dictates whether or not a coder may change something a physician has selected. Certainly we cannot change record content, but codes are not really parts of the record. Point being, some practices are content with the error rate their physicians produce and others (in my opinion more compliance-minded) do not let providers choose any codes, relying on full record abstraction, meaning the coder has autonomy to determine the claim's content.
As for billers changing codes, there are a lot of variables and considerations there. First, billers might have to "change" or crosswalk codes based on contract stipulations. In some places the coders know this; in others the billers have that responsibility. Too, there is the consideration of what triggers the change. Is it that the biller changes codes to get paid, because that is out of line with separation of duties and is a non-compliant practice? On the other hand, if the biller is abiding by published rules, then that may be acceptable. As a credentialed coder, I hesitate to encourage billers to make changes to the coding. If, however, I'm working with an experienced biller, or one who is certified in a relevant area, then I'd be more comfortable. The problem is that a great deal of bad habits have not been snuffed out of the billing side of the house, primarily because we don't require them to be credentialed (many, many times). Usually, I prefer for the coders to make changes; it keeps the division of responsibility clearer.
This is still going to be determined by internal policy. I cannot fathom that CMS or OIG have any real standards on who can do what in your practice. If that were the case, we'd have a lot of practices fined in short order.
