> The tax authorities cannot unilaterally change the law with "guidance".
Because the law generally allows but does not mandate enforcement against every violation, and because guidance provided by enforcement authorities can be used as a defense in enforcement actions, so long as the guidance provides what is in effect a structured exception to the law, but does not forbid anything not forbidden by the law, yes, they pretty much can in practice, even without explicit authority. And it is actually very common when external facts (including federal law) change faster than state/local process can keep up for enforcement agencies to use discretionary forbearance framed around specific guidance as a band-aid until adaptation of the underlying rules is in place.
Because the law generally allows but does not mandate enforcement against every violation, and because guidance provided by enforcement authorities can be used as a defense in enforcement actions, so long as the guidance provides what is in effect a structured exception to the law, but does not forbid anything not forbidden by the law, yes, they pretty much can in practice, even without explicit authority. And it is actually very common when external facts (including federal law) change faster than state/local process can keep up for enforcement agencies to use discretionary forbearance framed around specific guidance as a band-aid until adaptation of the underlying rules is in place.