#1: Abilities are set up from a master template and variants are created through inheritance.
#2: Abilities are bound to a character at runtime based on what pickups the character has currently equipped.
#3: Ability pickup items can spawn at runtime as semi-randomized variants of themselves, meaning procedurally generated loot, wherein the loot grants abilities when equipped.
Anything is possible. But yes, there’s nothing stopping you from writing an Ability system that modifies itself in some way during runtime. My plug-in, Able, does that for things like cooldown reduction, damage calculation, ability playback speed, etc. In Able’s case, you store the items on the player or what not, and Able simply asks the player to compute the value for it and returns that value to the internal systems.