Change existing UI element

[04348]

Hi !
I try to learn how to make addon for ESO, but the documentation about the API is very light ^^
So, I use LUA for a while so basic lua functions are not a problem, but can't get to really interact with the game

I want to make an addon which change the currency from gold to the mmo-famous gold/silver/copper in all UI element. Take gold value and display the formated string "g-s-c" is easy, but can someone explain me how to replace the money display on the original UI ?
Or is the only solution is to display over the UI ?
I've found a getcontrol() function, but unfortunaly ther's no doc on it

I'm a very noob in addon programming, so I try to make very simple (and useless ) addon, but I can't get how far we can get the UI control ^^

Thanks in advance !