No infinite gold but...
According to this Majesty 2 thread in Steam, you can gain gold each time you cast a Kingdom spell (i.e. Magic Lighting or Healing spells).
You just have to open
resource.pak file as it was a rar file, extract
/magic folder if needed). Then modify via Notepad. As simple as that.
I post the relevant part of the thread:
Open Resource.pak, extract the 2 files that are in gameData\magic
(spells.xml and spell.xsd) into x:\Steam\steamapps\common\majesty
Take into special consideration gamedata\magic\spells.xml open up with
notepad and change the cost of any spell to a negative number and you
gain gold whenever you cast a spell. e.g. spell name="magic_lightning"
This will grant me 2500 gold for each click.