A creature with a Bardic Inspiration die can roll it to add the result to an ability check, saving throw, or attack roll, while the Divination wizard's Portent feature overrides the roll before the roll is made.
Because the roll has never been made, does this mean that a roll replaced by Portent cannot be improved by the Bardic Inspiration die?
Best Answer
Yes, in fact you can.
5e rules designer Jeremy Crawford, gives an unofficial ruling in this tweet:
Portent only replaces the die roll, not the entire check; bonuses can then be added, including Bardic Inspiration.