Instead of Z clauses, can you remove and replace core clause sentences?

Answer

You can indeed, but what would you call this and how would you make sure such changes were properly incorporated into the contract? By pointing to the Z clauses in contract data part one and make sure all such clauses sit clearly under the heading ‘Option Z: Additional conditions of contract’, then there should be no doubt of their inclusion.

In addition you need to be aware that, if you are using an electronic licence to print your own contracts, the terms of that licence requires that if you make any changes from the standard text they have to be clearly annotated as such.