In the enlightening discussions I have read on the matter (and not in the popular media coverage on the whole) there is nothing unusual
about the transaction as far as current operating procedure is set down by the independent ECB.
It might be argued that the only precedent here is the volume of the bonds which might be transacted.
The ECB has for some time since the global crisis occured, AFAIK, provided the means for banks to avail of those rates and are providing unlimited liquidity facilities.
The unusual transaction is the one between the banks and the state run agency NAMA. It is, on paper , a clever way , as I see it of using the existing mechanisms afforded by the ECB. Are we saying that other EU countries would have to get the nod from ECB to do this ?