Will the High Representative come into office against the Lisbon Treaty rules?

Next week, the European Council will meet informally over a lunch, and the heads of state and government will decide over the two remaining top EU post, the European Council President and the High Representative for Foreign Affairs and Security Policy - but it looks as if the latter will be coming into office against the rules.

Grahnlaw quotes a press release of the the Finnish government

The Swedish Presidency has announced that the High Representative will become a member of the Commission immediately after his/her appointment and the current Commissioner of his/her nationality will step down from the office.

This looks like the European Council wants to act against the Lisbon Treaty where it is clearly written in Article 17 para 7 (on the election of the Commission):

The President, the High Representative of the Union for Foreign Affairs and Security Policy and the other members of the Commission shall be subject as a body to a vote of consent by the European Parliament. On the basis of this consent the Commission shall be appointed by the European Council, acting by a qualified majority.

Since the Parliament's vote shall happen before the European Council formally nominates the Commission, I don't see how it is possible that the High Representative can enter into office right after her/his nomination next Thursday.

This is especially not possible since it would be the old Commission that was formed under the Nice Treaty into which the person would be "nominated". The Nice Treaty doesn't even foresee the High Representative in the future format, so how can s/he enter into the old Commission while already being nominated according to Lisbon rules?

Legally s/he will probably "just" be part of the old Commission. Practically this means that s/he can shape her/his office before the new college will start its work, s/he will be the de facto Foreign Minister in a weak caretaker Commission and s/he won't be confirmed by the EP as all other Commissioners before. The person will thus lack the legitimacy foreseen in the old Treaty for Commissioners as well as the legality of the Lisbon Treaty.

This sounds to me like the Heads of State and Governments are trying to create a fait accompli:

By illegitimately (almost illegally) putting the person into her/his office before a Parliament vote, the governments put pressure on the EP so that it can't vote against the Commission later this year when the de facto Foreign Minister has already shaped her/his office and when the governments could argue that it would be "damaging" to remove the person from office after several months.