Eldritch Adept

Prerequisite: Spellcasting or Pact Magic feature
Studying occult lore, you have unlocked eldritch power within yourself: you learn one Eldritch Invocation option of your choice from the warlock class. If the invocation has a prerequisite of any kind, you can choose that invocation only if you're a warlock who meets the prerequisite.
Whenever you gain a level, you can replace the invocation with another one from the warlock class.