age_heir (number) (Country Tag) - Set heirs age country tag optional, indicates target.age_consort (number) (Country Tag) - Set consort's age to specified number country tag optional, indicates target.
age (number) - Changes the age of the game: 0 for Age of Discovery, 1 for Age of Reformation, 2 is Age of Absolutism and 3 is Age of Revolutions.add_opinion (Actor Country tag) (Target Country tag) - Adds 100 opinion of the target country to the actor country.add_heir (Country Tag) - Adds heir, kills existing one country tag optional, indicates target.add_permanent_claim (Province ID) (Country Tag) - Add permanent claim for specified province country tag optional, indicates target.add_claim (Province ID) (Country Tag) - Add specified claim country tag optional, indicates target.assimilate (Province ID) (Country Tag) - Change ownership, core, set culture and religion.mil (number) (Country tag) - Grants you the specified amount of military power points country tag optional, indicates target.dip (number) (Country tag) - Grants you the specified amount of diplomatic power points country tag optional, indicates target.legitimacy (number) (Country tag) - Sets the legitimacy of the current ruler to specified amount country tag optional, indicates target.prestige (number) (Country tag) - Grants you the specified amount of prestige country tag optional, indicates target.sailors (number) (Country tag) - Grants you the specified amount of sailors country tag optional, indicates target.manpower (number) (Country tag) - Grants you the specified amount of manpower country tag optional, indicates target.cash (number) (Country tag) - Grants you the specified amount of ducats country tag optional, indicates target.adm (number) (Country tag) - Grants you the specified amount of administrative power points country tag optional, indicates target.debug_mode - Displays province ID, country tag, and border distance when moving the mouse cursor over provinces.Here is a list of more useful EU4 console commands and cheats: Remember to remove the brackets when inputting them. You won't be able to use them in ironman games, which means you can't cheat your way to those harder achievements.
You can easily bring up Europa Universalis 4's console by simply pressing the tilde key (`), although this can vary, depending on your keyboard layout.