First you need to enable console. To do so for all game profiles go to gamedir\profiles\autoexec.cfg
Put this as last line
setvar dev_console_password = schwinge-des-todes
So it will look like this
...
//============================================================================
// Startup
mainmenu
setvar dev_console_password = schwinge-des-todes

Or you can enable console for only select profile by appending same line at end of user.cfg in 
C:\Documents and Settings\YourWinAcc\My Documents\My Games\Heroes of Might and Magic V\Profiles\YourProfile

Then you can use some cheats ingame. Press tilde key("`", "~") to bring down console. If it doesn't work for you because you don't have the key on your keyboard, can't find it because of foreign layout, whatever, you can always edit input.cfg in your user profile dir
//debug keys
bind show_console '`'
Edit this to something suitable for you then.

Basic thing console does is tell you what ai has been doing last turn.

Now, to cheats themselves.

Most complex 1 is add_skill 

add_skill takes skill-id or name as parameter, you can find list of all 150 skills/perks/abilities names and their ids in data\data.pak\scripts\advmap-startup.lua
HoMM 5 pak files are pkzip archives and as such you can access that lua scipt file using winrar/winzip etc(btw unpacking all packs will speed things up since game will access uncompressed data instead of looking in archives. You can even delete packs after that, but better move them somewhere else and keep them since we don't know if upcoming patches will modify archives or use overrides system).

So, for example:
add_skill Necromancy
Pretty self-explanatory.
or
add_skill 19
Will give perk pathfinding
You can add skills over limit it seems. E.g. more than 6 skills etc. Though you won\'t see them in ui, but will get benefits.

If you're really lazy and don't mind fortreiting easy performance boost, here's full list:

	-- Skill type IDs
	--
	-- Basic Skills
	SKILL_LOGISTICS = 1
	SKILL_WAR_MACHINES = 2
	SKILL_LEARNING = 3
	SKILL_LEADERSHIP = 4
	SKILL_LUCK = 5
	SKILL_OFFENCE = 6
	SKILL_DEFENCE = 7
	SKILL_SORCERY = 8
	SKILL_DESTRUCTIVE_MAGIC = 9
	SKILL_DARK_MAGIC = 10
	SKILL_LIGHT_MAGIC = 11
	SKILL_SUMMONING_MAGIC = 12
	-- Class skills
	SKILL_TRAINING   = 13
	SKILL_GATING     = 14
	SKILL_NECROMANCY = 15
	SKILL_AVENGER = 16
	SKILL_ARTIFICIER = 17
	SKILL_INVOCATION = 18
	-- Perks
	PERK_PATHFINDING = 19
	PERK_SCOUTING = 20
	PERK_NAVIGATION = 21
	PERK_FIRST_AID = 22
	PERK_BALLISTA = 23
	PERK_CATAPULT = 24
	PERK_INTELLIGENCE = 25
	PERK_SCHOLAR = 26
	PERK_EAGLE_EYE = 27
	PERK_RECRUITMENT = 28
	PERK_ESTATES = 29
	PERK_DIPLOMACY = 30
	PERK_RESISTANCE = 31
	PERK_LUCKY_STRIKE = 32
	PERK_FORTUNATE_ADVENTURER = 33
	PERK_TACTICS = 34
	PERK_ARCHERY = 35
	PERK_FRENZY = 36
	PERK_PROTECTION = 37
	PERK_EVASION = 38
	PERK_TOUGHNESS = 39
	PERK_MYSTICISM = 40
	PERK_WISDOM = 41
	PERK_ARCANE_TRAINING = 42
	PERK_MASTER_OF_ICE = 43
	PERK_MASTER_OF_FIRE = 44
	PERK_MASTER_OF_LIGHTNINGS = 45
	PERK_MASTER_OF_CURSES = 46
	PERK_MASTER_OF_MIND = 47
	PERK_MASTER_OF_SICKNESS = 48
	PERK_MASTER_OF_BLESSING = 49
	PERK_MASTER_OF_ABJURATION = 50
	PERK_MASTER_OF_WRATH = 51
	PERK_MASTER_OF_QUAKES = 52
	PERK_MASTER_OF_CREATURES = 53
	PERK_MASTER_OF_ANIMATION = 54
	-- Knight perks
	PERK_HOLY_CHARGE = 55
	PERK_PRAYER = 56
	PERK_EXPERT_TRAINER = 57
	-- Demonlord perks
	PERK_CONSUME_CORPSE = 58
	PERK_DEMONIC_FIRE = 59
	PERK_DEMONIC_STRIKE = 60
	-- Necromancer perks
	PERK_RAISE_ARCHERS          = 61
	PERK_NO_REST_FOR_THE_WICKED = 62
	PERK_DEATH_SCREAM           = 63
	-- Ranger perks
	PERK_MULTISHOT = 64
	PERK_SNIPE_DEAD = 65
	PERK_IMBUE_ARROW = 66
	-- Wizard perks 
	PERK_MAGIC_BOND = 67
	PERK_MELT_ARTIFACT = 68
	PERK_MAGIC_MIRROR = 69
	-- Warlock perks
	PERK_EMPOWERED_SPELLS = 70
	PERK_DARK_RITUAL = 71
	PERK_ELEMENTAL_VISION = 72
	-- Feats
	-- Knight
	KNIGHT_FEAT_ROAD_HOME = 73
	KNIGHT_FEAT_TRIPLE_BALLISTA = 74
	KNIGHT_FEAT_ENCOURAGE = 75
	KNIGHT_FEAT_RETRIBUTION = 76
	KNIGHT_FEAT_HOLD_GROUND = 77
	KNIGHT_FEAT_GUARDIAN_ANGEL = 78
	KNIGHT_FEAT_STUDENT_AWARD = 79
	KNIGHT_FEAT_GRAIL_VISION = 80
	KNIGHT_FEAT_CASTER_CERTIFICATE = 81
	KNIGHT_FEAT_ANCIENT_SMITHY = 82
	KNIGHT_FEAT_PARIAH = 83
	KNIGHT_FEAT_ELEMENTAL_BALANCE = 84
	KNIGHT_FEAT_ABSOLUTE_CHARGE = 85
	-- Demon Lord
	DEMON_FEAT_QUICK_GATING = 86
	DEMON_FEAT_MASTER_OF_SECRETS = 87
	DEMON_FEAT_TRIPLE_CATAPULT = 88
	DEMON_FEAT_GATING_MASTERY = 89
	DEMON_FEAT_CRITICAL_GATING = 90
	DEMON_FEAT_CRITICAL_STRIKE = 91
	DEMON_FEAT_DEMONIC_RETALIATION = 92
	DEMON_FEAT_EXPLODING_CORPSES = 93
	DEMON_FEAT_DEMONIC_FLAME = 94
	DEMON_FEAT_WEAKENING_STRIKE = 95
	DEMON_FEAT_FIRE_PROTECTION = 96
	DEMON_FEAT_FIRE_AFFINITY = 97
	DEMON_FEAT_ABSOLUTE_GATING = 98
	-- Necromancer
	NECROMANCER_FEAT_DEATH_TREAD = 99
	NECROMANCER_FEAT_LAST_AID = 100
	NECROMANCER_FEAT_LORD_OF_UNDEAD = 101
	NECROMANCER_FEAT_HERALD_OF_DEATH = 102
	NECROMANCER_FEAT_DEAD_LUCK = 103
	NECROMANCER_FEAT_CHILLING_STEEL = 104
	NECROMANCER_FEAT_CHILLING_BONES = 105
	NECROMANCER_FEAT_SPELLPROOF_BONES = 106
	NECROMANCER_FEAT_DEADLY_COLD = 107
	NECROMANCER_FEAT_SPIRIT_LINK = 108
	NECROMANCER_FEAT_TWILIGHT = 109
	NECROMANCER_FEAT_HAUNT_MINE = 110
	NECROMANCER_FEAT_ABSOLUTE_FEAR = 111
	-- Ranger
	RANGER_FEAT_DISGUISE_AND_RECKON = 112
	RANGER_FEAT_IMBUE_BALLISTA = 113
	RANGER_FEAT_CUNNING_OF_THE_WOODS = 114
	RANGER_FEAT_FOREST_GUARD_EMBLEM = 115
	RANGER_FEAT_ELVEN_LUCK = 116
	RANGER_FEAT_FOREST_RAGE = 117
	RANGER_FEAT_LAST_STAND = 118
	RANGER_FEAT_INSIGHTS = 119
	RANGER_FEAT_SUN_FIRE = 120
	RANGER_FEAT_SOIL_BURN = 121
	RANGER_FEAT_STORM_WIND = 122
	RANGER_FEAT_FOG_VEIL = 123
	RANGER_FEAT_ABSOLUTE_LUCK = 124
	-- Wizard
	WIZARD_FEAT_MARCH_OF_THE_MACHINES = 125
	WIZARD_FEAT_REMOTE_CONTROL = 126
	WIZARD_FEAT_ACADEMY_AWARD = 127
	WIZARD_FEAT_ARTIFICIAL_GLORY = 128
	WIZARD_FEAT_SPOILS_OF_WAR = 129
	WIZARD_FEAT_WILDFIRE = 130
	WIZARD_FEAT_SEAL_OF_PROTECTION = 131
	WIZARD_FEAT_COUNTERSPELL = 132
	WIZARD_FEAT_MAGIC_CUSHION = 133
	WIZARD_FEAT_SUPRESS_DARK  = 134
	WIZARD_FEAT_SUPRESS_LIGHT  = 135
	WIZARD_FEAT_UNSUMMON  = 136
	WIZARD_FEAT_ABSOLUTE_WIZARDY = 137
	-- warlock
	WARLOCK_FEAT_TELEPORT_ASSAULT = 138
	WARLOCK_FEAT_SHAKE_GROUND = 139
	WARLOCK_FEAT_DARK_REVELATION = 140
	WARLOCK_FEAT_FAST_AND_FURIOUS = 141
	WARLOCK_FEAT_LUCKY_SPELLS = 142
	WARLOCK_FEAT_POWER_OF_HASTE = 143
	WARLOCK_FEAT_POWER_OF_STONE = 144
	WARLOCK_FEAT_CHAOTIC_SPELLS = 145
	WARLOCK_FEAT_SECRETS_OF_DESTRUCTION = 146
	WARLOCK_FEAT_PAYBACK = 147
	WARLOCK_FEAT_ELITE_CASTERS = 148
	WARLOCK_FEAT_ELEMENTAL_OVERKILL	= 149
	WARLOCK_FEAT_ABSOLUTE_CHAINS = 150

add_army town nTownID, bUpgrade

Will fill all hero army slots with 10 creatures of town id specified. Second param is 0 or 1 which controls whether creatures are from upgraded dwellings or not.

Town ids:
HEAVEN = 0
PRESERVE = 1
ACADEMY = 2
DUNGEON = 3
NECRO = 4
INFERNO = 5

E.g.
add_army 5, 0
Will fill all hero army slots with 10 basic inferno creatures
add_army 4, 1 will fill hero army slots with 10 upgraded Necro creatures

Code Effect 
add_all_spells  Gives all spells to currently selected hero. Bypasses all skills reqs, for usage also. 
set_hero_luck_morale nLuck nMorale Sets luck and morale base values for current hero. For ex set_hero_luck_morale 5 3 
show_player_money playernumber Outputs resource quantities of specified player. So you can spy on ai. E.g. show_player_money 2 
show_hero_mp Shows detailed movement point stats for currently selected hero - exact quantity, stats for currently plotted path(how many points it\'ll take). 
add_exp quantity Adds quantity xp to currently selected hero. E.g. add_exp 5000 
clear_money Sets all your resources to 0 
add_gold quantity Sets current gold to quantity and zeroes out other resources. 
add_money Sets all resources except gold to quantity and sets gold to quantity*1000. So add_money 100 gives 100 of everything and 100000 gold.