the priesthood is changed but everlasting?

15 And thou shalt anoint them, as thou didst anoint their father, that they may minister unto me in the priest's office: for their anointing shall surely be an everlasting priesthood throughout their generations.

Heb. 8:13 In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away.
Heb. 9:1 ¶ Then verily the first covenant had also ordinances of divine service, and a worldly sanctuary.
Heb. 7:11 ¶ If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?
Heb. 7:12 For the priesthood being changed, there is made of necessity a change also of the law.

Doesnt sound that everlasting huh?

Well we know that all those rituals/ceremonies pointed to Jesus Christ, so the priesthood when our Saviour died and rose again, had to change (Heb 7:12).

I take the word 'everlasting' in this sense to be conditional. They would have an everlasting priesthood throughout their generations IF they were true to their calling and did not deviate from God's holy law. I was reading yesterday in Desire of Ages that if the high priest rent his priestly garments, 'by the Levitical law, this was prohibited under sentence of death.' (Pg 708) And when Caiaphas did just this he was disqualified from the priesthood. So then in that sense it can't be everlasting.