Heb 7:12 For the priesthood being changed, there is made of necessity a change also of the law.
G3331
metathesis
met-ath'-es-is
From G3346; transposition, that is, transferral (to heaven), disestablishment (of a law): - change, removing, translation.
Same word used here:
Heb 12:27 And this word, Yet once more, signifieth the removing of those things that are shaken, as of things that are made, that those things which cannot be shaken may remain.
Clarke:
There is made of necessity a change also of the law - The very essence of the Levitical law consisting in its sacrificial offerings; and as these could not confer perfection, could not reconcile God to man, purify the unholy heart, nor open the kingdom of heaven to the souls of men, consequently it must be abolished, according to the order of God himself; for he said, Sacrifice and offering, and burnt-offering, and sacrifice for sin, he would not; see Psa_40:6, Psa_40:7, compared with Heb_10:5-10, and with Psa_110:4, where it is evident God designed to change both the law and the priesthood, and to introduce Jesus as the only Priest and Sacrifice, and to substitute the Gospel system for that of the Levitical institutions.
So since we know the law was changed, let's go back to what Christ said:
Mat 5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Not even a "period" from the law could be removed or changed until "heaven and earth pass". The law did change and in a quite a large way thus we know that heaven and earth did pass away at the cross. This of course is a reference to a heaven and earth age passing not the actual Heaven or Earth disappearing or being replaced.