That chap from "answering-christianity" cracks me up.
The "lying pen of the scribes" is guilty not of changing the text of the law, but of false application of it. They are giving the wrong interpretation out of personal greed and because they fear men more than God. In effect, Jeremiah says that they don't "have" the Law because they don't KEEP the Law. It is not the physical presence of the Law or of the Temple that will avert God's wrath, but only obedience to his word. They did not corrupt the physical text of it, but they "handled" it falsely as 8:8 says. If the text they were working with hadn't been the Law anymore, then they could not have been accused of mishandling it ("it" = the Law).
"Having" the Law is no advantage whatsoever if you don't obey it. The endresult is the same as if you don't even have it. This is the consistent message of the Bible in many, many places.
For example you might have a detailed look at a similar address of judgment against the scribes by Jesus in Matthew 23. Let me explicitely quote a few verses here. Jesus starts out his harsh words of condemnation (taking up nearly all of chapter 23) with:
2 The teachers of the law and the Pharisees sit in Moses' seat.
3 So you must obey them and do everything they tell you. But do not do what they do, for they do not practice what they preach.