Europa Universalis Cheats

Here's the steps I discovered accidentally (believe it or not)
1. Go into Single Player.
2. Go back to Main Menu.
3. Go into Multiplayer.
4. Enter ANY name at all.
5. Back to Main Menu.
6. Single Player again.
7. Click on the game you want to switch sides on.
8. Shields on top should be 'clickable' and select what major power
you want to be.
9. Smile!!!!!!!!!!!! :)

Works well when you are losing a war (with a major country)!

Use one of the following values with the "event [event number]" code:
 
Result Event number
Creates revolt in random province 1
Creates revolt in random colony 2
Religious revolt 3
Religion 7
Heretics 8
Death 9
Excellent 10
Insanity 11
Scandal 12
Gift 13
Gold lost 14
Obscurantism 15
Except year 16
Colonist 17
Demand 18
Bank 20
Stock exchange 21
Company of trade 22
Port closure 23
Diplomacy 24
Pressure 25
Col Dyn 26
Inventions 27
Merchants 28
Stolen sea charts 29
Plague 30
Naval disaster 31
Desertion 32
Land tech 33
Naval tech 34
Enthu army 35
Enthu navy 36
Annex 37
Agriculture 38
Fire 39
Good Gov 40
Poor Gov 41
Unhappy Clergy 42
Unhappy Artists 43
Unhappy Peasants 44
Unhappy Merchant 45
Mineral 46
Crisis 47
Corruption 48
Deflation 49
Dip insult 50
Favored trade nation 51
Industrial development 52
New center of trade 53
Trade restrictions 54
Fortification 55
Explorer 56
Conquistador 57

Return to the main menu while in single player mode.
Select multi-player mode, enter any name, then return to the main
menu. Select single player mode again, and choose the previous
game. Click on the shields at the top of the screen to change
nations.
Strategy: by Duken008

While playing the game, push F12, then submit one of the codes below in the console window to enable that particular cheat code:

Toggle control of all military units - richelieu <on or off>
Toggle fog of war - pappenheim
All provinces explored - columbus
Land technology level increased - gustavus
Naval technology level increased - drake
Infrastructure level increased - cromwell
Trade level increased - polo
Stability set to +3 - oranje
Toggle all natives - cortez <on or off>
Toggle revolts - alba <on or off>
Toggle A.I. war declaration - tilly <on or off>
Add 50,000 ducats to treasury - montezuma
Add 10 colonists - pocahontas
Add 10 merchants - dagama
Add 10 diplomats - vatican
Add 10.000 population to capital province - swift
Treaty of Tordesillas mode - tordesillas
Reformation mode; allow nations to convert to Protestantism - luther
John Calvin mode; allow nations to convert to Reformed Christianity - calvin
Council Of Trent mode; cancel John Calvin mode - trent
Troop limits - peterthegreat
More cannon fodder troops - russianhordes
Toggle God mode - difrules <on or off>
Japan closed - shogun
Create indicated event - event <event number>

(Use with EVENT cheat) Event 1 = Creates Revolt in random province
Event 2 = Creates Revolt in random colony
Event 3 = Rel rev
Event 7 = Religion
Event 8 = Heretics
Event 9 = Death
Event 10 = Excellent
Event 11 = Insanity
Event 12 = Scandal
Event 13 = Gift
Event 14 = Gold lost
Event 15 = Obscuritism
Event 16 = Except year
Event 17 = Colonist
Event 18 = Demand
Event 20 = Bank
Event 21 = Stock exchange
Event 22 = Company of trae
Event 23 = Port closure
Event 24 = Diplomacy
Event 25 = pressure
Event 26 = Col Dyn
Event 27 = Inventions
Event 28 = Merchants
Event 29 = Stolen sea charts
Event 30 = Plague
Event 31 = Naval disaster
Event 32 = Dessertion
Event 33 = Land tech
Event 34 = naval tech
Event 35 = Enthu army
Event 36 = Enthu navy
Event 37 = Annex
Event 38 = Agriculture
Event 39 = Fire
Event 40 = Good Gov
Event 41 = Poor Gov
Event 42 = Unhappy Clergy
Event 43 = Unhappy Artis
Event 44 = Unhappy Peasants
Event 45 = Unhappy Merchant
Event 46 = Minerral
Event 47 = Crisis
Event 48 = Corruption
Event 49 = Defaltion
Event 50 = Dip insult
Event 51 = Favored trade nation
Event 52 = Indust development
Event 53 = New centre of trade
Event 54 = Frade restrictions
Event 55 = Fortification
Event 56 = Explorer
Event 57 = Conquistador

I've only tried this with version 1.09eu so it may not work with earlier versions. To increase your technology levels quickly and really play like a god, hit event 49 (deflation) at least 5 or 6 times and then use the normal increase Technology codes (Gustavus, Drake, Cromwell, Polo). Each use of it should increase your technology level by 1 FULL step if you have decreased your inflation enough. Also found that you can actually make money upgrading with manufactories with the deflation set to a negative amount.

Also event 57 is the fortification effort, not event 55, and it only works on your core provinces, the ones with the country's shield on the political map.