Given that a deed of variation of a Will or intestacy is a fiction for tax purposes only and does not affect property law, then if a deed of variation purports to include a fictional will then presumably any trustees purportedly appointed under the fictional will are not, in reality, appointed as trustees?
The only fiction is that for tax purposes the deed is treated as varying the will. As a matter of law, the deed is an agreement between the parties to it and all of its provisions have effect. That means that if the deed of variation appoints trustees, those trustees are appointed.
I agree with Josh and would say also that any appointment “so called” as executors is ineffective.