What is the basis that allows the changing of Halakha? Halakha/Jewish Law states that in the normal course of things we may not permit what Judaism has forbidden, nor may we repeal or abolish what is obligatory.

So, for Christians who do not keep Halakha, what is the basis of not following the law? I get that Christians can add to the laws but to not follow all of the laws appears to be something that we cannot do.

Jesus said:

Matthew 5:17-18 New International Version (NIV)

The Fulfillment of the Law

“Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished.

Kosher is an example of a law we don't keep but is part of Halakha. This question is not limited to Kosher, I am just making an example.