The clause dealing with contract instructions states… provided that such contract instructions shall not substantially change the scope of the works.

The principal agent and the parties should agree what constitutes a change of scope in terms of the project – and agree the scope / cost / timing implications (the revised date for practical completion, adjustment of the contract valuepenalties) etc before making such a decision. The principal agent cannot unilaterally issue such a contract instruction

See: 6.1P-17.1.1./17.1.2; 5.0P- 17.1.1/17.1.2