This question was inspired by the Question "Can Cutting Words cancel a critical hit?" According to a tweet by Jeremy Crawford, the Bardic inspiration ability cannot negate a critical hit. In fact he goes so far as to say that no penalty or modifier can do so:
Cutting Words can't nullify a critical hit—no bonus or penalty can (PH, 194). [Overrides a deleted 12/3 tweet]
This brings into question the Portent ability of a Diviner Wizard:
When you finish a long rest, roll two d20s and record the numbers rolled. You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.
Can this ability, since it is replacing instead of modifying the roll, negate a critical hit?