I'll provide some information, if I may.
What you're stating is exactly right in the case of a regular bill. If it were clause 2, let's say, of a regular bill amending an act, then that would be the case.
Here, however, clause 120 of this bill is a new act. It's considered a clause, and you can amend any part of a clause. That's why we can amend the definitions in it.