= Small fix mods =

Please tell me if there are any cheat codes in Heroes, and if so, how to enable them.

Of course, there are!
To activate them, you need to do the following:
Find the "profiles" folder in the directory where the game is installed.
In this folder, find the file "autoexec_a2.cfg".
Open it for editing; you will see the following content:
//================================================== ==========================
// User config

setvar credits_move_speed = 40

Add the cheat panel activator:

//================================================== ==========================
// User config

setvar dev_console_password = schwinge-des-todes

show_heroes_mana 1 ... this is the activator for displaying the hero's mana, which is very useful!

setvar credits_move_speed = 40

Then, in the "profiles" folder, find the "default_profile" folder and open the "input_a2.cfg" file for editing.
Find "// obsolete, but strictly need for compability with some interfaces"
and add bind show_console '`'
It will look like this:
// obsolete, but strictly need for compability with some interfaces
bind close_window 'ESC'
bind confirm_action    'ENTER'
bind confirm_action    'NUM_ENTER'
bind show_console '`'

Load the game, and now, when you press the "tilde/apostrophe/Ё" button, the panel for entering cheat commands will open.
To activate the codes on any map (as far as I remember, the activation of the cheat panel is saved in the map's save file), you need to enter "enable_cheats" and press Enter; a message will appear saying that the cheats have been successfully activated!
To check if everything is working, launch the game and choose Necropolis, then select the hero Kaspar.
Press the "tilde", enter enable_cheats, press Enter, enter @AddHeroCreatures("Gles", CREATURE_DEMILICH, 2), and press Enter.
Kaspar's army will "miraculously" have two liches!
P.S.
By the way, here here and here here you can find more information about cheats!