Can the Employer change the site boundaries after contract award, would this be a CE, and can they instruct works outside of the boundaries of the site if the change is not agreed?
Site boundaries, in common with any other aspect of the contract, can be changed by agreement between the contracting parties. The definition of site boundary is found in contract data part one and there is non unilateral right (that is a right of one party alone) to alter the content of contract data. An agreed change to the site boundary wouldn’t fall within the definition of a compensation event and that mechanism isn’t really suitable for such a change in any event. Any impact on the works should be considered as par6t of the agreement changing the site boundary, as if it were a mini contract in its own right.
The last part of your question is the most interesting, from a contract point of view. The PM can change the Works Information and there is no restriction that I can see to say that can only be within the site boundary. So, in theory, the answer must be yes work outside the site boundary can be instructed via a change in the Work Information. However, that may create a number of issues around access etc. How you would go about valuing a change to the WI instructing works outside the site boundary would be complex I suspect.
Further, there would need to remain sufficient connection to the original subject matter of the work to be allowable. For example, in a contract to build a warehouse a CE to instruct the construction of a dual carriageway adjacent to the building would almost certainly not be enforceable.