Yes, the Contractor can change the method shown on the Accepted Programme for the circumstances you describe. In doing so the Contractor may need to resubmit the Activity Schedule in accordance with clause 55.3 (the value of the Activity Schedule being unamended).
The Contractor may also be required to submit the new design in accordance with clause 21 depending upon the requirements of the Scope. From a design perspective, the Contractor’s obligation is to design the works stated in the Scope (see 21.1). Provided the design complies with the Scope and the law then it should be accepted.
No, the change in design does not require a change in Scope (provided the design complies with the Scope) and the PM would not need to instruct a change. If the revised design does not comply with the Scope then the PM can reject (not accept) it.
The Contractor may also be required to submit the new design in accordance with clause 21 depending upon the requirements of the Scope. From a design perspective, the Contractor’s obligation is to design the works stated in the Scope (see 21.1). Provided the design complies with the Scope and the law then it should be accepted.
No, the change in design does not require a change in Scope (provided the design complies with the Scope) and the PM would not need to instruct a change. If the revised design does not comply with the Scope then the PM can reject (not accept) it.