I'm not exactly sure how changes to ability scores in combat affect abilities that have uses based on the modifier for that that skill.
For example take a bard with a Charisma score of 18 that has already used his 4 Bardic Inspirations. He then draws the Star card from the Deck of Many things. He uses it to increase his Charisma to 20, making his Charisma modifier +5.
As the number of Bardic Inspirations is determined by the Charisma modifier, would its increase to +5 give him an additional use of Bardic Inspiration?
On the other hand, suppose the bard has an Ioun stone taking his Charisma to 20. He uses 4 Inspirations, and then steps in a Antimagic Field, disabling the Ioun stone and reducing his Charisma to 18(+4). Would he have one available Bardic Inspiration or none?