Is the Croatian Solution legally possible?

In order to reassure Ireland on certain legal matters raised in the Lisbon Treaty referendum campaign, the plan was to attach the legally binding guarantees to the Croatian Accession treaty. The idea was that this would prevent the need to reopen the ratification process all over Europe.

However, doubts have been raised about the legal possibility of this route: MEP Andrew Duff has suggested that general revisions of the main treaties cannot be achieved through accession treaties. He cites the Danish opt outs being included in the Amsterdam Treaty as an example.

If this is true, then it's a big blow to the strategy of the Irish Government in obtaining the legal guarantees politically (though not necessarily legally) vital to getting a Yes vote in the second Lisbon Treaty campaign.

Meanwhile, the government has re-re-re-re-re-re-re-re-re-affirmed (again), that it will not be complacent in the next referendum. Why are these statements still treated like news? It was issued during a EU debate in the Dáil, where it was shockingly revealed that more work needed to be done on the guarantees.