NEC 3 ECS: Contract amendments by Contractor

I understand all the bolt ons and options and x and z clauses a main Contractor can use to tailor a contract to a specific project

But can a basic ECS option B be amended by the main contractor? If so where would we expect to see the amendments laid out/detailed?

Any amendments to standard option B clauses or even additional clauses would need to be identified as Z clauses. In contract data part 1 it will state if there are Z clauses, and if so should in turn state where within your contract documents those amendments are. They will either be a list of amendments to read along side the standard contract, or a complete version of the contract with the changes embedded in them.