According to the Episcopal Conference of England and Wales, the transferred Holydays of Obligation are transferred in the Extraordinary Rite, as well as the Ordinary Rite. They know because they submitted a dubium to the Pontifical Commission Ecclesia Dei.
Canon Law is quite clear that Episcopal Conferences have the right to transfer (or, God Forbid! suppress) Holydays of Obligation:
Can. 1246 §1. Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be observed in the universal Church as the primordial holy day of obligation. The following days must also be observed: the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Body and Blood of Christ, Holy Mary the Mother of God, her Immaculate Conception, her Assumption, Saint Joseph, Saint Peter and Saint Paul the Apostles, and All Saints.
§2. With the prior approval of the Apostolic See, however, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.
However, they need the prior approval of the Apostolic See. It would be interesting to see the manner in which this approval has been sought for the Extraordinary Rite and the consequent form of approval, given that it had been understood hitherto that the Extraordinary Rite had its own calendar. Is the Pontifical Commission Ecclesia Dei competent in this regard?
Much more importantly, this is on a par with the leaking of the terna for Westminster. This is the old gang hoping that it is asserting its authority, but, just in case, leaving a series of mantraps for anybody who is not part of the magic circle who ends up in Archbishop's House.
If we weren't all much more civilised, I'd wonder if the Episcopal Conference was calling the Curia out. Is this the start of a transition to warfare? Is Eccleston Square a bit like the Greater London Authority, preparing to lose its great helmsman?